Clenbuterol
In a two-week randomized crossover, clenbuterol increased lean mass by 0.91 kg. Fat mass and sprint performance did not improve, while aerobic capacity and maximum work fell. Short studies also found higher energy expenditure and muscle glucose uptake. Controlled trials report tremor, cramps, palpitations, and higher heart rate; misuse reports include myocardial injury and severe metabolic toxicity.
Long-acting beta2-adrenergic agonist without US human approval
- A two-week healthy-men trial found 0.91 kg more lean mass, no fat loss, no sprint benefit, and lower aerobic capacity.
- A single-exposure study raised energy expenditure and fat oxidation for 140 minutes; repeated-dose trials did not show fat loss.
- Small disease trials show muscle or functional signals, but attrition, baseline imbalance, and poor tolerability limit them.
- Controlled studies repeatedly report tremor, cramps, palpitations, and higher heart rate.
- There is no FDA-approved human product in the United States; the US Ventipulmin product is for horses.
Is clenbuterol an FDA-approved human medicine?
FDA lists no approved human use in the United States. Ventipulmin is a restricted US horse product whose label says it is not for humans. A 2023 EMA document listed national human products in Bulgaria, Germany, and Italy; those listings were country-level, not centralized EU authorization.
| Record | What it establishes | What it does not |
|---|---|---|
| FDA human status | No US human approval | No claim about every foreign country |
| Ventipulmin NADA | Restricted veterinary use in horses | Human approval or a human regimen |
| EMA 2023 list | Named national products in BG, DE, and IT | Central EU authorization or current marketing everywhere |
FDA/DOJ · clenbuterol is not US-approved for humans
Official enforcement statement
United States Attorney's Office, District of New Jersey; posted by the US Food and Drug Administration. New Jersey Husband and Wife Admit Selling Misbranded and Unapproved New Drugs. 2022. Press Release 22-104.
The official release identifies clenbuterol as sold in foreign markets but not approved by FDA for human use in the United States.
- Participants / model
- United States regulatory status
- Treatment
- Not applicable
- Study design
- Official enforcement and regulatory statement
An enforcement release is not a global product register; the EMA national-authorisation list separately documents some European products.
Read the original sourceFDA animal approval · horses only, not humans
FDA veterinary approval summary
US Food and Drug Administration, Center for Veterinary Medicine. Freedom of Information Summary, NADA 140-973, Ventipulmin Syrup (clenbuterol hydrochloride). Approved May 11, 1998.
FDA approved oral clenbuterol syrup for management of airway obstruction in horses not intended for food. The record explicitly says the product is not for human use and warns of cardiovascular effects after accidental ingestion.
- Participants / model
- Horses with airway obstruction; human warning is occupational/accidental exposure
- Treatment
- Veterinary oral clenbuterol hydrochloride syrup
- Follow-up
- Veterinary treatment programs up to 30 days
- Study design
- Veterinary NADA effectiveness and safety dossier
Veterinary approval is not evidence of human approval, human dosing, or human benefit-risk.
Read the original sourceEMA 2023 list · selected national human authorizations
European regulatory product list
European Medicines Agency. Clenbuterol: List of nationally authorised medicinal products, procedure PSUSA/00000794/202209. EMA/294361/2023. May 25, 2023.
The list names human clenbuterol tablet or syrup products authorized nationally in Bulgaria, Germany, and Italy at that regulatory procedure date.
- Participants / model
- National product authorizations in named European states
- Treatment
- Oral tablets or syrup
- Follow-up
- Regulatory snapshot dated May 25, 2023
- Study design
- Official list supporting a periodic safety update procedure
This is a dated national-authorisation list, not a centralized EU authorization and not proof that every listed presentation remains marketed in every country in 2026.
Read the original sourceWhat does clenbuterol do?
It is a beta2-adrenergic agonist with bronchodilator, skeletal-muscle, cardiovascular, and metabolic effects. The receptor class explains both the respiratory activity and the same tremor, tachycardia, potassium, glucose, and cardiac liabilities seen in toxicity.
PubChem CID 2783 · clenbuterol identity
Government substance database
National Library of Medicine. PubChem Compound Summary for CID 2783, Clenbuterol.
Identifies clenbuterol base as C12H18Cl2N2O, molecular weight 277.19 g/mol, CID 2783.
- Participants / model
- Not applicable
- Treatment
- Not applicable
- Follow-up
- Living database record
- Study design
- Curated chemical identity record
Chemical identity does not establish human approval, safety, or formulation quality.
Read the original source19 adults with asthma · old oral bronchodilator trial
Double-blind crossover trial
Y. Salorinne, B. Stenius, P. Tukiainen, and H. Poppius. European Journal of Clinical Pharmacology. 1975. PMID 9295.
In 19 adults with moderately severe asthma treated over 24 days, oral clenbuterol and oral salbutamol improved peak flow, rescue inhaler use, and recorded symptoms compared with placebo.
- Participants / model
- 19 adult outpatients with moderately severe asthma
- Treatment
- Oral clenbuterol, oral salbutamol, and placebo
- Follow-up
- 24-day crossover treatment period
- Study design
- Double-blind crossover comparison
This tiny 1975 oral bronchodilator study predates modern inhaled rescue and controller standards and does not answer enhancement safety.
Read the original source34 emergency presentations · metabolic and myocardial toxicity
Multistate toxicology outbreak case series
Robert S. Hoffman, Barbara M. Kirrane, Steven M. Marcus, and the Clenbuterol Study Investigators. Annals of Emergency Medicine. 2008. PMID 18501476.
Thirty-four probable or confirmed emergency presentations followed exposure to clenbuterol-adulterated heroin; 13 met confirmed criteria. Findings included tachycardia, hypotension, hyperglycemia, hypokalemia, increased lactate, and biochemical myocardial injury in six patients.
- Participants / model
- 34 probable or confirmed emergency presentations in five US states; 13 confirmed
- Treatment
- Uncontrolled exposure to clenbuterol-adulterated heroin
- Follow-up
- 6-month outbreak
- Study design
- Descriptive poison-center and health-department outbreak study
Co-exposure to heroin, unknown product composition, and outbreak ascertainment prevent incidence estimates; the series still documents a coherent beta-agonist toxicity pattern.
Read the original sourceDoes clenbuterol burn fat or improve performance?
The modern healthy-men trial found a short lean-mass signal without fat loss or better performance. Eleven men completed the clenbuterol period and ten the placebo period. Lean mass was 0.91 kg higher, fat mass differed by 0.00 kg, six-second sprint power did not improve, VO2max was 249 mL/min lower, and maximum work was 16 W lower.
| Outcome | Treatment difference | Meaning |
|---|---|---|
| Lean mass | +0.91 kg; 95% CI 0.02 to 1.81 | Short two-week signal; retained gain and muscle size were not measured |
| Fat mass | 0.00 kg; 95% CI -0.52 to 0.52 | No fat-loss result |
| Six-second sprint | Peak -36 W, p=.135; mean -21 W, p=.402 | No detected sprint benefit |
| Aerobic capacity | VO2max -249 mL/min; maximum work -16 W | About 7% and 4% lower, respectively |
| Cardiac structure | No detected left-ventricular-mass change | Two weeks and a tiny cohort cannot establish chronic safety |
Thirteen healthy men entered; 11 completed the active period and 10 the placebo period. Anti Doping Denmark funded the study.
11 healthy men · lean mass up, fitness down, no fat loss
Randomized placebo-controlled crossover trial
Morten Hostrup, Lukas Moesgaard, Mads Fischer, Kate Aiko Wickham, Mads Pleshardt, Andreas Breenfeldt Andersen, Jacob Bejder, Martin Thomassen, Jens J. Nielsen, Yvette Dehnes, Jens Bangsbo, Nikolai B. Nordsborg, and Søren Jessen. The Journal of Physiology. 2025. PMID 40946331.
Lean mass was 0.91 kg higher after clenbuterol (95% CI 0.02 to 1.81; p=0.046), fat mass was unchanged, VO2max was 249 mL/min lower, and maximum work was 16 W lower. Acute heart rate rose 10 beats/min and muscle beta2 response was attenuated by day 14.
- Participants / model
- 13 healthy men aged 18 to 40 enrolled; 11 completed the clenbuterol period and 10 the placebo period
- Treatment
- Oral clenbuterol versus placebo
- Follow-up
- Two 2-week periods separated by a 3-week washout
- Study design
- Randomized placebo-controlled crossover physiology trial
- Funding
- Anti Doping Denmark
Tiny male-only crossover with 13 enrolled, 11 active-period completers, and 10 placebo-period completers. Two weeks cannot establish rare, chronic, or structural cardiac risk; diet and activity were not tightly controlled.
Read the original sourceWhat do the thermogenesis and glucose studies show?
A single-exposure study in six young men raised energy expenditure and fat oxidation for 140 minutes while maximal voluntary torque fell 4%. Two small crossover trials found muscle glucose-uptake signals. Neither produced a clinical diabetes outcome, and the four-week trial in people with overweight or obesity found no change in whole-body insulin sensitivity, weight, fat mass, lean mass, or overnight energy expenditure.
| Study | Result | Limit |
|---|---|---|
| Jessen 2020; n=6 healthy men; single exposure | Resting energy expenditure +21%, fat oxidation +39%, maximal torque -4%; glucose +30%, lactate +90%, insulin +130% | 140 minutes; no fat-loss or training outcome |
| Van Beek 2023; n=11 healthy men; two-week crossover | Insulin-stimulated glucose disposal 46.6 vs 41.2 µmol/kg/min, p=.032; body composition unchanged | Mechanism study; no diabetes or long-term outcome; heart rate rose about 11 bpm |
| Van Lier 2026; n=14 with overweight/obesity; four-week crossover | Vastus uptake +15%, p=.072; hamstring +13%, p=.039; whole-body insulin sensitivity p=.926 | Primary muscle outcome missed p<.05; body composition and overnight metabolism were null; heart rate rose about 5 bpm |
| Eijsvogel 2024; small healthy and Parkinson cohorts | Selected memory and tracking endpoints improved; repeated-dose adaptive tracking +1.58 percentage points | Many endpoints, no multiplicity correction, inconsistent results, and sponsor involvement |
Jessen et al. · acute thermogenesis study
Acute human physiology study
Jessen S, Solheim SA, Jacobson GA, Eibye K, Bangsbo J, Nordsborg NB, Hostrup M. Drug Testing and Analysis. 2020;12(5):610-618. PMID 31887249. DOI 10.1002/dta.2755.
In six young men over 140 minutes, resting energy expenditure rose 21%, fat oxidation 39%, mTOR phosphorylation 121%, and PKA-substrate phosphorylation 35%. Maximal voluntary torque fell 4%; glucose rose 30%, lactate 90%, insulin 130%, and free fatty acids 180%.
- Participants / model
- 6 young healthy men
- Treatment
- Single oral clenbuterol exposure
- Follow-up
- 140 minutes
- Study design
- Acute uncontrolled before-after human physiology study
- Funding
- Anti Doping Denmark
The study measured acute flux and signaling, not fat loss, training, or long-term safety.
Read the original sourceVan Beek et al. · healthy-men glucose study
Randomized placebo-controlled crossover trial
Van Beek SMM, Bruls YMH, Vanweert F, et al. Nature Communications. 2023;14:225. PMID 36635304. DOI 10.1038/s41467-023-35798-5.
Insulin-stimulated glucose disposal was 46.6 versus 41.2 µmol/kg/min, a 13% difference (p=.032). Body weight and composition were unchanged, heart rate rose about 11 bpm, and 5/11 men reported side effects.
- Participants / model
- 12 healthy men randomized; 11 completed after one COVID-related dropout
- Treatment
- Clenbuterol versus placebo
- Follow-up
- Two two-week crossover periods
- Study design
- Randomized double-blind placebo-controlled crossover
The study measured mechanism, not diabetes prevention or long-term benefit. One author disclosed stock in Atrogi AB.
Read the original sourceVan Lier et al. · 2026 metabolic crossover
Randomized placebo-controlled crossover trial
Van Lier PMG, van de Weijer T, Vanweert F, et al. Nature Communications. 2026;17:5483. PMID 42014715. DOI 10.1038/s41467-026-71897-9.
Vastus-lateralis glucose uptake rose 15% but missed conventional significance (p=.072); hamstring uptake rose 13% (p=.039). Whole-body insulin sensitivity was unchanged (p=.926), as were weight, fat mass, lean mass, and overnight energy expenditure. Heart rate rose about 5 bpm.
- Participants / model
- 14 adults with overweight or obesity; 11 men and 3 postmenopausal women
- Treatment
- Clenbuterol versus placebo
- Follow-up
- Two four-week crossover periods
- Study design
- Randomized double-blind placebo-controlled crossover
- Funding
- Netherlands Enterprise Agency EuroStars program
One author disclosed Atrogi AB stock. The authors said cardiovascular effects make clenbuterol unsuitable for long-term diabetes-drug development.
Read the original sourceEijsvogel et al. · exploratory cognition program
Early-phase crossover and parallel clinical program
Eijsvogel PPNM, Borghans LGJM, Prins S, et al. Journal of Parkinson's Disease. 2024;14:947-959. PMID 39213090. DOI 10.3233/JPD-240039.
Selected immediate-recall and adaptive-tracking endpoints improved in small healthy-volunteer groups; the repeated-dose tracking difference was 1.58 percentage points. Many endpoints were null, one incongruent-response measure worsened, and repeated exposure raised heart rate by about 11.5 bpm.
- Participants / model
- Several small healthy-volunteer and Parkinson-disease cohorts
- Treatment
- Clenbuterol, other beta-acting drugs, or placebo
- Follow-up
- Single exposure or 7 days, depending on study part
- Study design
- Exploratory crossover and parallel early-phase studies
- Funding
- CuraSen Therapeutics
There was no multiplicity correction; sponsor employees, consultants, and site personnel were authors. The small Parkinson groups do not establish a disease outcome.
Read the original sourceHow do animal hypertrophy results compare with human data?
Rodent studies can produce large skeletal-muscle effects under systemic exposure. In one 41-rat experiment, skeletal-muscle hypertrophy came with 18% to 20% cardiac hypertrophy. That is a warning signal, not proof of human cardiac growth. The two-week healthy trial found no left-ventricular-mass change, but it was too small and short to settle chronic structural risk.
41 rats · skeletal and cardiac hypertrophy
Preclinical animal study
M. Petrou, D. G. Wynne, K. R. Boheler, and M. H. Yacoub. Circulation. 1995. PMID 7586459.
In 41 male Sprague-Dawley rats, subcutaneous clenbuterol increased hindlimb and latissimus muscle hypertrophy indices and also produced 18% to 20% cardiac hypertrophy.
- Participants / model
- 41 male Sprague-Dawley rats
- Treatment
- Subcutaneous clenbuterol versus saline
- Follow-up
- 2 or 5 weeks
- Study design
- Controlled rat hypertrophy and gene-expression study
Rat systemic exposure and organ hypertrophy cannot establish a favorable human anabolic benefit-risk balance; cardiac growth is not a benign surrogate.
Read the original source11 healthy men · lean mass up, fitness down, no fat loss
Randomized placebo-controlled crossover trial
Morten Hostrup, Lukas Moesgaard, Mads Fischer, Kate Aiko Wickham, Mads Pleshardt, Andreas Breenfeldt Andersen, Jacob Bejder, Martin Thomassen, Jens J. Nielsen, Yvette Dehnes, Jens Bangsbo, Nikolai B. Nordsborg, and Søren Jessen. The Journal of Physiology. 2025. PMID 40946331.
Lean mass was 0.91 kg higher after clenbuterol (95% CI 0.02 to 1.81; p=0.046), fat mass was unchanged, VO2max was 249 mL/min lower, and maximum work was 16 W lower. Acute heart rate rose 10 beats/min and muscle beta2 response was attenuated by day 14.
- Participants / model
- 13 healthy men aged 18 to 40 enrolled; 11 completed the clenbuterol period and 10 the placebo period
- Treatment
- Oral clenbuterol versus placebo
- Follow-up
- Two 2-week periods separated by a 3-week washout
- Study design
- Randomized placebo-controlled crossover physiology trial
- Funding
- Anti Doping Denmark
Tiny male-only crossover with 13 enrolled, 11 active-period completers, and 10 placebo-period completers. Two weeks cannot establish rare, chronic, or structural cardiac risk; diet and activity were not tightly controlled.
Read the original sourceDo the old asthma trials make clenbuterol a modern respiratory choice?
A 1975 crossover in 19 adults found that oral clenbuterol and salbutamol improved peak flow and symptoms versus placebo. The trial predates today's inhaled rescue and controller standards, so it cannot rank modern respiratory options.
19 adults with asthma · old oral bronchodilator trial
Double-blind crossover trial
Y. Salorinne, B. Stenius, P. Tukiainen, and H. Poppius. European Journal of Clinical Pharmacology. 1975. PMID 9295.
In 19 adults with moderately severe asthma treated over 24 days, oral clenbuterol and oral salbutamol improved peak flow, rescue inhaler use, and recorded symptoms compared with placebo.
- Participants / model
- 19 adult outpatients with moderately severe asthma
- Treatment
- Oral clenbuterol, oral salbutamol, and placebo
- Follow-up
- 24-day crossover treatment period
- Study design
- Double-blind crossover comparison
This tiny 1975 oral bronchodilator study predates modern inhaled rescue and controller standards and does not answer enhancement safety.
Read the original sourceFDA/DOJ · clenbuterol is not US-approved for humans
Official enforcement statement
United States Attorney's Office, District of New Jersey; posted by the US Food and Drug Administration. New Jersey Husband and Wife Admit Selling Misbranded and Unapproved New Drugs. 2022. Press Release 22-104.
The official release identifies clenbuterol as sold in foreign markets but not approved by FDA for human use in the United States.
- Participants / model
- United States regulatory status
- Treatment
- Not applicable
- Study design
- Official enforcement and regulatory statement
An enforcement release is not a global product register; the EMA national-authorisation list separately documents some European products.
Read the original sourceEMA 2023 list · selected national human authorizations
European regulatory product list
European Medicines Agency. Clenbuterol: List of nationally authorised medicinal products, procedure PSUSA/00000794/202209. EMA/294361/2023. May 25, 2023.
The list names human clenbuterol tablet or syrup products authorized nationally in Bulgaria, Germany, and Italy at that regulatory procedure date.
- Participants / model
- National product authorizations in named European states
- Treatment
- Oral tablets or syrup
- Follow-up
- Regulatory snapshot dated May 25, 2023
- Study design
- Official list supporting a periodic safety update procedure
This is a dated national-authorisation list, not a centralized EU authorization and not proof that every listed presentation remains marketed in every country in 2026.
Read the original sourceWhat do muscle-disease studies show?
Small studies in denervated muscle, heart failure, Pompe disease, spinal and bulbar muscular atrophy, and ALS report biological or functional signals in patients. High attrition, baseline imbalance, uncontrolled designs, within-group analyses, and adverse-effect withdrawals keep those results tied to their disease settings.
| Study | Result | Critical limit |
|---|---|---|
| Maltin 1993; 20 men after meniscectomy | Relative recovery and a contralateral-leg signal | Absolute strength did not significantly differ between randomized groups |
| Kamalakkannan 2008; heart failure; 19 enrolled, 17 completed | Lean mass rose; strength rose 27% active and 14% placebo within groups | Two active participants withdrew; endurance and exercise duration fell; no clean between-group strength result |
| Jiang 2011; traumatic denervation; 71 randomized | Smaller muscle-fiber and EMG losses in per-protocol analyses | Only 15 active/17 placebo remained for EMG and 12/13 for biopsy; no patient-function endpoint |
| Koeberl 2018; Pompe; 13 randomized, 11 completed | Within-active-group walking, inspiratory-pressure, motor-test, and muscle-glycogen signals | Large baseline imbalance, underpowered, and no direct arm comparison |
| Querin 2013; SBMA; 20 open label, 16 completed | Walking and vital-capacity signals from baseline | No control; other functional scores were null |
| Li 2023; ALS; n=25 open label | Authors reported slower back-calculated ALSFRS-R and FVC slopes | 14 withdrew early and 13 withdrew for adverse effects; no randomization, blinding, or concurrent control |
Maltin et al. · post-meniscectomy strength study
Randomized double-blind clinical trial
Maltin CA, Delday MI, Watson JS, et al. Clinical Science. 1993;84(6):651-654. PMID 8334811. DOI 10.1042/cs0840651.
The study reported relative recovery and a contralateral-leg within-group signal after meniscectomy; absolute strength did not differ significantly between randomized groups.
- Participants / model
- 20 healthy male patients after medial meniscectomy
- Treatment
- Clenbuterol or placebo
- Follow-up
- Four weeks plus washout
- Study design
- Randomized double-blind clinical trial
A postoperative rehabilitation result does not establish healthy strength enhancement.
Read the original sourceKamalakkannan et al. · heart-failure trial
Randomized placebo-controlled pilot trial
Kamalakkannan G, Petrilli CM, George I, et al. Journal of Heart and Lung Transplantation. 2008;27(4):457-461. PMID 18374884. DOI 10.1016/j.healun.2008.01.013.
Lean mass increased. Maximum strength rose 27% in the active arm and 14% in placebo within groups, while endurance and exercise duration fell.
- Participants / model
- 19 patients with NYHA class II to III chronic heart failure; 10 active and 9 placebo; 17 completed
- Treatment
- Clenbuterol or placebo
- Follow-up
- 12 weeks
- Study design
- Small randomized placebo-controlled pilot
Two active participants withdrew for adverse effects, and the study did not establish a clear absolute between-group strength benefit.
Read the original sourceJiang et al. · denervated-muscle trial
Randomized double-blind placebo-controlled trial
Jiang GL, Gu YD, Zhang LY, Shen LY, Yu C, Xu JG. ISRN Pharmaceutics. 2011;2011:981254. PMID 22389867. DOI 10.5402/2011/981254.
Among per-protocol repeat biopsies, type-I fiber-area loss was 413 versus 687 µm² and type-II loss 512 versus 821 µm²; EMG fibrillation-potential loss was also smaller with clenbuterol.
- Participants / model
- 71 patients with traumatic brachial-plexus denervation randomized
- Treatment
- Clenbuterol or placebo
- Follow-up
- Three months
- Study design
- Randomized double-blind placebo-controlled trial with per-protocol analysis
Only 15 active and 17 placebo participants remained in the EMG analysis, and 12 and 13 remained in the biopsy analysis; 19 per arm were excluded for compliance or loss, plus one active participant after reinnervation. No patient-function benefit was shown. The corresponding author also listed Allergan R&D; the report contains no explicit funding declaration.
Read the original sourceKoeberl et al. · randomized Pompe pilot
Randomized double-blind placebo-controlled phase 1/2 trial
Koeberl DD, Case LE, Smith EC, et al. Molecular Therapy. 2018;26(9):2304-2314. PMID 30025991. DOI 10.1016/j.ymthe.2018.06.023.
At week 52 the active arm changed 6-minute walk distance by +16 m (p=.08), predicted distance +3% (p=.03), inspiratory pressure +8%, quick motor score +7 points, gait/stairs score +2 points, and vastus glycogen -50%.
- Participants / model
- 13 adults with late-onset Pompe disease on enzyme replacement; 8 active and 5 placebo; 11 completed
- Treatment
- Adjunctive clenbuterol or placebo
- Follow-up
- 52 weeks
- Study design
- Randomized double-blind placebo-controlled phase 1/2 pilot
- Funding
- Academic and disease-research support; author and institutional technology and industry interests were disclosed
Baseline groups differed markedly, the trial was underpowered, and the paper emphasized within-group change instead of direct arm comparisons.
Read the original sourceQuerin et al. · open SBMA pilot
Open-label pilot trial
Querin G, D'Ascenzo C, Peterle E, et al. Neurology. 2013;80(23):2095-2098. PMID 23645595. DOI 10.1212/WNL.0b013e318295d766.
Six-minute walk distance and forced vital capacity improved from baseline among completers; MRC and ALSFRS-R measures did not.
- Participants / model
- 20 patients with spinal and bulbar muscular atrophy; 16 completed 12 months
- Treatment
- Open-label clenbuterol
- Follow-up
- 12 months
- Study design
- Uncontrolled open-label pilot
No concurrent comparator was used, and the disease-specific result does not establish healthy performance.
Read the original sourceLi et al. · high-withdrawal ALS pilot
Open-label clinical trial
Li X, Koeberl DD, Lutz MW, Bedlack R. Journal of Clinical Neuromuscular Disease. 2023;24(4):214-221. PMID 37219865. DOI 10.1097/CND.0000000000000438.
Authors reported slower ALSFRS-R and FVC slopes during treatment, but 14/25 withdrew early and 13 withdrawals were due to adverse effects. Pretreatment slopes were back-calculated by assuming normal scores at disease onset.
- Participants / model
- 25 people with ALS
- Treatment
- Open-label clenbuterol
- Follow-up
- 24 weeks
- Study design
- Uncontrolled open-label trial using back-calculated pretreatment slopes
- Funding
- Donations from one patient's family; investigators disclosed multiple industry relationships and institutional financial interests
The design and attrition prevent a causal efficacy claim.
Read the original sourceWhat does documented human toxicity look like?
Short controlled studies repeatedly report tremor, cramps, palpitations, headache, restlessness, insomnia, and higher heart rate. Surveillance and misuse reports add tachycardia, hypokalemia, hyperglycemia, hypotension, chest pain, and myocardial injury. These reports establish a coherent toxicity pattern, while unknown doses, co-use, and passive reporting prevent an incidence estimate.
| Record | Findings | Limit |
|---|---|---|
| Van Beek 2023 | 5/11 reported side effects: tremor 5, muscle ache/tension/cramps 4, anxiety/restlessness 2, headache 2 | Small screened healthy cohort |
| Van Lier 2026 | Tremor 3/14, headache 2/14, palpitations/increased heart rate 2/14, cramps 2/14; heart rate about 5 bpm higher | Four weeks; small screened cohort |
| Pompe trial | Insomnia 5/8, spasms 4/8, tremor 4/8, palpitations/increased heart rate 2/8; two dose reductions | Eight treated patients cannot estimate uncommon harm |
| CDC/Hoffman outbreaks | 26 CDC cases with 24 hospitalizations; later 34 presentations with 13 confirmed and 6 myocardial injuries | Heroin co-exposure, unknown dose, passive ascertainment |
| Spiller 2013 | 13 poison-center cases, 11 involving weight-loss/bodybuilding intent; two myocardial injuries; effects could last beyond 24 hours | Case series, no exposed denominator |
| Bonenti 2025 survey | 197 AAS-plus-clenbuterol vs 949 AAS-only men: adjusted OR 2.76 for heart concern, 1.73 mood fluctuation, 1.61 excitability | Cross-sectional self-report, drug and behavior confounding, no clenbuterol-only arm |
Van Beek et al. · healthy-men glucose study
Randomized placebo-controlled crossover trial
Van Beek SMM, Bruls YMH, Vanweert F, et al. Nature Communications. 2023;14:225. PMID 36635304. DOI 10.1038/s41467-023-35798-5.
Insulin-stimulated glucose disposal was 46.6 versus 41.2 µmol/kg/min, a 13% difference (p=.032). Body weight and composition were unchanged, heart rate rose about 11 bpm, and 5/11 men reported side effects.
- Participants / model
- 12 healthy men randomized; 11 completed after one COVID-related dropout
- Treatment
- Clenbuterol versus placebo
- Follow-up
- Two two-week crossover periods
- Study design
- Randomized double-blind placebo-controlled crossover
The study measured mechanism, not diabetes prevention or long-term benefit. One author disclosed stock in Atrogi AB.
Read the original sourceVan Lier et al. · 2026 metabolic crossover
Randomized placebo-controlled crossover trial
Van Lier PMG, van de Weijer T, Vanweert F, et al. Nature Communications. 2026;17:5483. PMID 42014715. DOI 10.1038/s41467-026-71897-9.
Vastus-lateralis glucose uptake rose 15% but missed conventional significance (p=.072); hamstring uptake rose 13% (p=.039). Whole-body insulin sensitivity was unchanged (p=.926), as were weight, fat mass, lean mass, and overnight energy expenditure. Heart rate rose about 5 bpm.
- Participants / model
- 14 adults with overweight or obesity; 11 men and 3 postmenopausal women
- Treatment
- Clenbuterol versus placebo
- Follow-up
- Two four-week crossover periods
- Study design
- Randomized double-blind placebo-controlled crossover
- Funding
- Netherlands Enterprise Agency EuroStars program
One author disclosed Atrogi AB stock. The authors said cardiovascular effects make clenbuterol unsuitable for long-term diabetes-drug development.
Read the original sourceKoeberl et al. · randomized Pompe pilot
Randomized double-blind placebo-controlled phase 1/2 trial
Koeberl DD, Case LE, Smith EC, et al. Molecular Therapy. 2018;26(9):2304-2314. PMID 30025991. DOI 10.1016/j.ymthe.2018.06.023.
At week 52 the active arm changed 6-minute walk distance by +16 m (p=.08), predicted distance +3% (p=.03), inspiratory pressure +8%, quick motor score +7 points, gait/stairs score +2 points, and vastus glycogen -50%.
- Participants / model
- 13 adults with late-onset Pompe disease on enzyme replacement; 8 active and 5 placebo; 11 completed
- Treatment
- Adjunctive clenbuterol or placebo
- Follow-up
- 52 weeks
- Study design
- Randomized double-blind placebo-controlled phase 1/2 pilot
- Funding
- Academic and disease-research support; author and institutional technology and industry interests were disclosed
Baseline groups differed markedly, the trial was underpowered, and the paper emphasized within-group change instead of direct arm comparisons.
Read the original sourceCDC outbreak · 26 cases, 24 hospitalized
Multistate public-health outbreak investigation
Centers for Disease Control and Prevention. Morbidity and Mortality Weekly Report. 2005;54(32):793 to 796.
CDC identified 26 cases in five states and 24 hospitalizations; eight were laboratory-confirmed. In the eight-case southern cluster, all had palpitations, heart rates of 120 to 141, and potassium of 1.9 to 2.8 mmol/L; six had hypotension.
- Participants / model
- 26 people with atypical sympathomimetic illness after heroin exposure in five US states
- Treatment
- Unregulated heroin exposure contaminated with clenbuterol
- Follow-up
- January to April 2005 outbreak surveillance
- Study design
- Passive case finding, medical-record review, interviews, and toxicology
- Funding
- US public-health investigation
Only eight cases were analytically confirmed; heroin co-exposure, unknown dose/purity, and passive ascertainment prevent incidence or dose-response estimates.
Read the original source34 emergency presentations · metabolic and myocardial toxicity
Multistate toxicology outbreak case series
Robert S. Hoffman, Barbara M. Kirrane, Steven M. Marcus, and the Clenbuterol Study Investigators. Annals of Emergency Medicine. 2008. PMID 18501476.
Thirty-four probable or confirmed emergency presentations followed exposure to clenbuterol-adulterated heroin; 13 met confirmed criteria. Findings included tachycardia, hypotension, hyperglycemia, hypokalemia, increased lactate, and biochemical myocardial injury in six patients.
- Participants / model
- 34 probable or confirmed emergency presentations in five US states; 13 confirmed
- Treatment
- Uncontrolled exposure to clenbuterol-adulterated heroin
- Follow-up
- 6-month outbreak
- Study design
- Descriptive poison-center and health-department outbreak study
Co-exposure to heroin, unknown product composition, and outbreak ascertainment prevent incidence estimates; the series still documents a coherent beta-agonist toxicity pattern.
Read the original sourceSpiller et al. · poison-center misuse series
Poison-center case series
Spiller HA, James KJ, Scholzen S, Borys DJ. Substance Abuse. 2013;34(3):306-312. PMID 23844963. DOI 10.1080/08897077.2013.772083.
Thirteen poison-center cases were described; 11 involved bodybuilding or weight-loss intent, symptoms could persist beyond 24 hours, and two cases had myocardial injury.
- Participants / model
- 13 reported clenbuterol misuse or abuse cases
- Treatment
- Uncontrolled market-product exposure
- Follow-up
- Clinical course beyond 24 hours in some cases
- Study design
- Descriptive poison-center case series
There is no exposed-user denominator, and dose, co-use, and product identity limit attribution.
Read the original sourceBonenti et al. · Global Drug Survey comparison
Cross-sectional self-report study
Bonenti B, Puljević C, Steve V, et al. Performance Enhancement & Health. 2025;13:100356. DOI 10.1016/j.peh.2025.100356.
Among 1,146 male 2024 Global Drug Survey respondents, 197 reported AAS plus clenbuterol and 949 AAS without clenbuterol. Age-adjusted odds ratios were 2.76 for negative heart effects, 1.73 for rapid mood fluctuation, and 1.61 for irrational excitability; restlessness/irritability was 1.36 (p=.122).
- Participants / model
- 1,146 male AAS users in the 2024 Global Drug Survey
- Treatment
- Self-reported AAS plus clenbuterol versus AAS without clenbuterol
- Follow-up
- Prior 12-month use
- Study design
- Cross-sectional anonymous survey comparison
- Funding
- No specific grant
Self-selection, younger age, earlier or heavier AAS use, other substances, missing dose data, recall, and the absence of a clenbuterol-only arm prevent causal or drug-to-drug safety conclusions.
Read the original sourceOld human PK · long persistence, uncertain precision
Human and animal pharmacokinetic study
I. Yamamoto, K. Iwata, and M. Nakashima. Journal of Pharmacobio-Dynamics. 1985. PMID 4045696.
Twelve healthy men participated. Nine supplied single-exposure curves and three the repeated-exposure series. Plasma peaks occurred about 2 to 3 hours, the estimated half-life was about 35 hours, steady state appeared by day 4, and about 20% of unchanged drug was recovered in urine by 72 hours.
- Participants / model
- 12 healthy male volunteers; single-exposure n=9 and repeated-exposure n=3
- Treatment
- Oral clenbuterol hydrochloride
- Follow-up
- Single exposure and short repeated exposure
- Study design
- Pharmacokinetic sampling with enzyme immunoassay
- Funding
- Clenbuterol hydrochloride and tablets were supplied by Teijin Co. Ltd.
Small 1980 volunteer study using an enzyme immunoassay. The repeated-exposure group was three and one later high-exposure mean contained two observations; the 35-hour estimate is historical and product-specific.
Read the original sourceIs the often-quoted long half-life precise?
The 1985 paper enrolled 12 healthy men. Single-exposure curves used nine men, three at each tested exposure; repeated-exposure curves used three. Plasma peaks occurred about 2 to 3 hours after oral tablets and the terminal decline gave an estimated 35-hour half-life. The estimate comes from a small study using an older enzyme immunoassay; repeated-exposure figure means sometimes contain only two participants.
| Cohort | Finding | Precision limit |
|---|---|---|
| 12 healthy men total; n=9 single exposure, n=3 repeated exposure | Tmax about 2 to 3 hours; half-life about 35 hours; steady state around day 4 | 1980 sampling, old enzyme immunoassay, tiny repeated-exposure group and some two-person means |
Old human PK · long persistence, uncertain precision
Human and animal pharmacokinetic study
I. Yamamoto, K. Iwata, and M. Nakashima. Journal of Pharmacobio-Dynamics. 1985. PMID 4045696.
Twelve healthy men participated. Nine supplied single-exposure curves and three the repeated-exposure series. Plasma peaks occurred about 2 to 3 hours, the estimated half-life was about 35 hours, steady state appeared by day 4, and about 20% of unchanged drug was recovered in urine by 72 hours.
- Participants / model
- 12 healthy male volunteers; single-exposure n=9 and repeated-exposure n=3
- Treatment
- Oral clenbuterol hydrochloride
- Follow-up
- Single exposure and short repeated exposure
- Study design
- Pharmacokinetic sampling with enzyme immunoassay
- Funding
- Clenbuterol hydrochloride and tablets were supplied by Teijin Co. Ltd.
Small 1980 volunteer study using an enzyme immunoassay. The repeated-exposure group was three and one later high-exposure mean contained two observations; the 35-hour estimate is historical and product-specific.
Read the original sourceAre newer trials complete?
The cited trial records list two disease trials as recruiting: an estimated 30-person open-label FSHD study and an estimated 90-person placebo-controlled SBMA study. A planned 60-person muscle-memory and resistance-training study had unknown status after January 2023. None had posted results. A 2026 KLHL41 biomarker paper appears to reuse the 2025 healthy cohort and is not independent replication.
Recent Chinese pediatric reports study a fixed ambroxol-plus-clenbuterol respiratory product, so they cannot isolate clenbuterol or answer adult body-composition and performance questions. The cited records contain no independent Russian-language administered-human enhancement result.
ClinicalTrials.gov · current clenbuterol trial status
Clinical trial registry record set
ClinicalTrials.gov listed 12 clenbuterol intervention records.
NCT06721299 was recruiting with estimated n=30 in FSHD; NCT06169046 was recruiting with estimated n=90 in SBMA; NCT05692856 had unknown status after January 2023 with estimated n=60. None had posted results.
- Participants / model
- Registered clenbuterol studies
- Treatment
- Clenbuterol in disease or muscle-study protocols
- Study design
- Exact-intervention registry coverage
- Funding
- Sponsors vary by record
A 2026 KLHL41 biomarker report appears to reuse the completed NCT03860870 cohort and is not independent clinical replication. Recent Chinese fixed ambroxol-plus-clenbuterol studies cannot isolate clenbuterol. The cited records contain no independent Russian-language administered-human enhancement result.
Read the original sourceJiang et al. · denervated-muscle trial
Randomized double-blind placebo-controlled trial
Jiang GL, Gu YD, Zhang LY, Shen LY, Yu C, Xu JG. ISRN Pharmaceutics. 2011;2011:981254. PMID 22389867. DOI 10.5402/2011/981254.
Among per-protocol repeat biopsies, type-I fiber-area loss was 413 versus 687 µm² and type-II loss 512 versus 821 µm²; EMG fibrillation-potential loss was also smaller with clenbuterol.
- Participants / model
- 71 patients with traumatic brachial-plexus denervation randomized
- Treatment
- Clenbuterol or placebo
- Follow-up
- Three months
- Study design
- Randomized double-blind placebo-controlled trial with per-protocol analysis
Only 15 active and 17 placebo participants remained in the EMG analysis, and 12 and 13 remained in the biopsy analysis; 19 per arm were excluded for compliance or loss, plus one active participant after reinnervation. No patient-function benefit was shown. The corresponding author also listed Allergan R&D; the report contains no explicit funding declaration.
Read the original sourceIs clenbuterol prohibited in tested sport?
Yes. The 2026 WADA list places clenbuterol in S1.2 other anabolic agents, prohibited at all times in and out of competition.
WADA 2026 · clenbuterol prohibited at all times
International sport regulation
World Anti-Doping Agency. The 2026 Prohibited List. In force January 1, 2026.
The 2026 list includes clenbuterol under S1.2 other anabolic agents, a class prohibited at all times in and out of competition.
- Participants / model
- Athletes subject to the World Anti-Doping Code
- Treatment
- Regulatory classification, not treatment
- Follow-up
- 2026 season
- Study design
- International anti-doping standard
Sport status is separate from national medicine authorization.
Read the original sourceStudies and sources
FDA/DOJ · clenbuterol is not US-approved for humans
Official enforcement statement
United States Attorney's Office, District of New Jersey; posted by the US Food and Drug Administration. New Jersey Husband and Wife Admit Selling Misbranded and Unapproved New Drugs. 2022. Press Release 22-104.
The official release identifies clenbuterol as sold in foreign markets but not approved by FDA for human use in the United States.
- Participants / model
- United States regulatory status
- Treatment
- Not applicable
- Study design
- Official enforcement and regulatory statement
An enforcement release is not a global product register; the EMA national-authorisation list separately documents some European products.
Read the original sourceFDA animal approval · horses only, not humans
FDA veterinary approval summary
US Food and Drug Administration, Center for Veterinary Medicine. Freedom of Information Summary, NADA 140-973, Ventipulmin Syrup (clenbuterol hydrochloride). Approved May 11, 1998.
FDA approved oral clenbuterol syrup for management of airway obstruction in horses not intended for food. The record explicitly says the product is not for human use and warns of cardiovascular effects after accidental ingestion.
- Participants / model
- Horses with airway obstruction; human warning is occupational/accidental exposure
- Treatment
- Veterinary oral clenbuterol hydrochloride syrup
- Follow-up
- Veterinary treatment programs up to 30 days
- Study design
- Veterinary NADA effectiveness and safety dossier
Veterinary approval is not evidence of human approval, human dosing, or human benefit-risk.
Read the original sourceEMA 2023 list · selected national human authorizations
European regulatory product list
European Medicines Agency. Clenbuterol: List of nationally authorised medicinal products, procedure PSUSA/00000794/202209. EMA/294361/2023. May 25, 2023.
The list names human clenbuterol tablet or syrup products authorized nationally in Bulgaria, Germany, and Italy at that regulatory procedure date.
- Participants / model
- National product authorizations in named European states
- Treatment
- Oral tablets or syrup
- Follow-up
- Regulatory snapshot dated May 25, 2023
- Study design
- Official list supporting a periodic safety update procedure
This is a dated national-authorisation list, not a centralized EU authorization and not proof that every listed presentation remains marketed in every country in 2026.
Read the original source11 healthy men · lean mass up, fitness down, no fat loss
Randomized placebo-controlled crossover trial
Morten Hostrup, Lukas Moesgaard, Mads Fischer, Kate Aiko Wickham, Mads Pleshardt, Andreas Breenfeldt Andersen, Jacob Bejder, Martin Thomassen, Jens J. Nielsen, Yvette Dehnes, Jens Bangsbo, Nikolai B. Nordsborg, and Søren Jessen. The Journal of Physiology. 2025. PMID 40946331.
Lean mass was 0.91 kg higher after clenbuterol (95% CI 0.02 to 1.81; p=0.046), fat mass was unchanged, VO2max was 249 mL/min lower, and maximum work was 16 W lower. Acute heart rate rose 10 beats/min and muscle beta2 response was attenuated by day 14.
- Participants / model
- 13 healthy men aged 18 to 40 enrolled; 11 completed the clenbuterol period and 10 the placebo period
- Treatment
- Oral clenbuterol versus placebo
- Follow-up
- Two 2-week periods separated by a 3-week washout
- Study design
- Randomized placebo-controlled crossover physiology trial
- Funding
- Anti Doping Denmark
Tiny male-only crossover with 13 enrolled, 11 active-period completers, and 10 placebo-period completers. Two weeks cannot establish rare, chronic, or structural cardiac risk; diet and activity were not tightly controlled.
Read the original source19 adults with asthma · old oral bronchodilator trial
Double-blind crossover trial
Y. Salorinne, B. Stenius, P. Tukiainen, and H. Poppius. European Journal of Clinical Pharmacology. 1975. PMID 9295.
In 19 adults with moderately severe asthma treated over 24 days, oral clenbuterol and oral salbutamol improved peak flow, rescue inhaler use, and recorded symptoms compared with placebo.
- Participants / model
- 19 adult outpatients with moderately severe asthma
- Treatment
- Oral clenbuterol, oral salbutamol, and placebo
- Follow-up
- 24-day crossover treatment period
- Study design
- Double-blind crossover comparison
This tiny 1975 oral bronchodilator study predates modern inhaled rescue and controller standards and does not answer enhancement safety.
Read the original sourceOld human PK · long persistence, uncertain precision
Human and animal pharmacokinetic study
I. Yamamoto, K. Iwata, and M. Nakashima. Journal of Pharmacobio-Dynamics. 1985. PMID 4045696.
Twelve healthy men participated. Nine supplied single-exposure curves and three the repeated-exposure series. Plasma peaks occurred about 2 to 3 hours, the estimated half-life was about 35 hours, steady state appeared by day 4, and about 20% of unchanged drug was recovered in urine by 72 hours.
- Participants / model
- 12 healthy male volunteers; single-exposure n=9 and repeated-exposure n=3
- Treatment
- Oral clenbuterol hydrochloride
- Follow-up
- Single exposure and short repeated exposure
- Study design
- Pharmacokinetic sampling with enzyme immunoassay
- Funding
- Clenbuterol hydrochloride and tablets were supplied by Teijin Co. Ltd.
Small 1980 volunteer study using an enzyme immunoassay. The repeated-exposure group was three and one later high-exposure mean contained two observations; the 35-hour estimate is historical and product-specific.
Read the original source34 emergency presentations · metabolic and myocardial toxicity
Multistate toxicology outbreak case series
Robert S. Hoffman, Barbara M. Kirrane, Steven M. Marcus, and the Clenbuterol Study Investigators. Annals of Emergency Medicine. 2008. PMID 18501476.
Thirty-four probable or confirmed emergency presentations followed exposure to clenbuterol-adulterated heroin; 13 met confirmed criteria. Findings included tachycardia, hypotension, hyperglycemia, hypokalemia, increased lactate, and biochemical myocardial injury in six patients.
- Participants / model
- 34 probable or confirmed emergency presentations in five US states; 13 confirmed
- Treatment
- Uncontrolled exposure to clenbuterol-adulterated heroin
- Follow-up
- 6-month outbreak
- Study design
- Descriptive poison-center and health-department outbreak study
Co-exposure to heroin, unknown product composition, and outbreak ascertainment prevent incidence estimates; the series still documents a coherent beta-agonist toxicity pattern.
Read the original source41 rats · skeletal and cardiac hypertrophy
Preclinical animal study
M. Petrou, D. G. Wynne, K. R. Boheler, and M. H. Yacoub. Circulation. 1995. PMID 7586459.
In 41 male Sprague-Dawley rats, subcutaneous clenbuterol increased hindlimb and latissimus muscle hypertrophy indices and also produced 18% to 20% cardiac hypertrophy.
- Participants / model
- 41 male Sprague-Dawley rats
- Treatment
- Subcutaneous clenbuterol versus saline
- Follow-up
- 2 or 5 weeks
- Study design
- Controlled rat hypertrophy and gene-expression study
Rat systemic exposure and organ hypertrophy cannot establish a favorable human anabolic benefit-risk balance; cardiac growth is not a benign surrogate.
Read the original sourceWADA 2026 · clenbuterol prohibited at all times
International sport regulation
World Anti-Doping Agency. The 2026 Prohibited List. In force January 1, 2026.
The 2026 list includes clenbuterol under S1.2 other anabolic agents, a class prohibited at all times in and out of competition.
- Participants / model
- Athletes subject to the World Anti-Doping Code
- Treatment
- Regulatory classification, not treatment
- Follow-up
- 2026 season
- Study design
- International anti-doping standard
Sport status is separate from national medicine authorization.
Read the original sourcePubChem CID 2783 · clenbuterol identity
Government substance database
National Library of Medicine. PubChem Compound Summary for CID 2783, Clenbuterol.
Identifies clenbuterol base as C12H18Cl2N2O, molecular weight 277.19 g/mol, CID 2783.
- Participants / model
- Not applicable
- Treatment
- Not applicable
- Follow-up
- Living database record
- Study design
- Curated chemical identity record
Chemical identity does not establish human approval, safety, or formulation quality.
Read the original sourceCDC outbreak · 26 cases, 24 hospitalized
Multistate public-health outbreak investigation
Centers for Disease Control and Prevention. Morbidity and Mortality Weekly Report. 2005;54(32):793 to 796.
CDC identified 26 cases in five states and 24 hospitalizations; eight were laboratory-confirmed. In the eight-case southern cluster, all had palpitations, heart rates of 120 to 141, and potassium of 1.9 to 2.8 mmol/L; six had hypotension.
- Participants / model
- 26 people with atypical sympathomimetic illness after heroin exposure in five US states
- Treatment
- Unregulated heroin exposure contaminated with clenbuterol
- Follow-up
- January to April 2005 outbreak surveillance
- Study design
- Passive case finding, medical-record review, interviews, and toxicology
- Funding
- US public-health investigation
Only eight cases were analytically confirmed; heroin co-exposure, unknown dose/purity, and passive ascertainment prevent incidence or dose-response estimates.
Read the original sourceJessen et al. · acute thermogenesis study
Acute human physiology study
Jessen S, Solheim SA, Jacobson GA, Eibye K, Bangsbo J, Nordsborg NB, Hostrup M. Drug Testing and Analysis. 2020;12(5):610-618. PMID 31887249. DOI 10.1002/dta.2755.
In six young men over 140 minutes, resting energy expenditure rose 21%, fat oxidation 39%, mTOR phosphorylation 121%, and PKA-substrate phosphorylation 35%. Maximal voluntary torque fell 4%; glucose rose 30%, lactate 90%, insulin 130%, and free fatty acids 180%.
- Participants / model
- 6 young healthy men
- Treatment
- Single oral clenbuterol exposure
- Follow-up
- 140 minutes
- Study design
- Acute uncontrolled before-after human physiology study
- Funding
- Anti Doping Denmark
The study measured acute flux and signaling, not fat loss, training, or long-term safety.
Read the original sourceVan Beek et al. · healthy-men glucose study
Randomized placebo-controlled crossover trial
Van Beek SMM, Bruls YMH, Vanweert F, et al. Nature Communications. 2023;14:225. PMID 36635304. DOI 10.1038/s41467-023-35798-5.
Insulin-stimulated glucose disposal was 46.6 versus 41.2 µmol/kg/min, a 13% difference (p=.032). Body weight and composition were unchanged, heart rate rose about 11 bpm, and 5/11 men reported side effects.
- Participants / model
- 12 healthy men randomized; 11 completed after one COVID-related dropout
- Treatment
- Clenbuterol versus placebo
- Follow-up
- Two two-week crossover periods
- Study design
- Randomized double-blind placebo-controlled crossover
The study measured mechanism, not diabetes prevention or long-term benefit. One author disclosed stock in Atrogi AB.
Read the original sourceVan Lier et al. · 2026 metabolic crossover
Randomized placebo-controlled crossover trial
Van Lier PMG, van de Weijer T, Vanweert F, et al. Nature Communications. 2026;17:5483. PMID 42014715. DOI 10.1038/s41467-026-71897-9.
Vastus-lateralis glucose uptake rose 15% but missed conventional significance (p=.072); hamstring uptake rose 13% (p=.039). Whole-body insulin sensitivity was unchanged (p=.926), as were weight, fat mass, lean mass, and overnight energy expenditure. Heart rate rose about 5 bpm.
- Participants / model
- 14 adults with overweight or obesity; 11 men and 3 postmenopausal women
- Treatment
- Clenbuterol versus placebo
- Follow-up
- Two four-week crossover periods
- Study design
- Randomized double-blind placebo-controlled crossover
- Funding
- Netherlands Enterprise Agency EuroStars program
One author disclosed Atrogi AB stock. The authors said cardiovascular effects make clenbuterol unsuitable for long-term diabetes-drug development.
Read the original sourceEijsvogel et al. · exploratory cognition program
Early-phase crossover and parallel clinical program
Eijsvogel PPNM, Borghans LGJM, Prins S, et al. Journal of Parkinson's Disease. 2024;14:947-959. PMID 39213090. DOI 10.3233/JPD-240039.
Selected immediate-recall and adaptive-tracking endpoints improved in small healthy-volunteer groups; the repeated-dose tracking difference was 1.58 percentage points. Many endpoints were null, one incongruent-response measure worsened, and repeated exposure raised heart rate by about 11.5 bpm.
- Participants / model
- Several small healthy-volunteer and Parkinson-disease cohorts
- Treatment
- Clenbuterol, other beta-acting drugs, or placebo
- Follow-up
- Single exposure or 7 days, depending on study part
- Study design
- Exploratory crossover and parallel early-phase studies
- Funding
- CuraSen Therapeutics
There was no multiplicity correction; sponsor employees, consultants, and site personnel were authors. The small Parkinson groups do not establish a disease outcome.
Read the original sourceJiang et al. · denervated-muscle trial
Randomized double-blind placebo-controlled trial
Jiang GL, Gu YD, Zhang LY, Shen LY, Yu C, Xu JG. ISRN Pharmaceutics. 2011;2011:981254. PMID 22389867. DOI 10.5402/2011/981254.
Among per-protocol repeat biopsies, type-I fiber-area loss was 413 versus 687 µm² and type-II loss 512 versus 821 µm²; EMG fibrillation-potential loss was also smaller with clenbuterol.
- Participants / model
- 71 patients with traumatic brachial-plexus denervation randomized
- Treatment
- Clenbuterol or placebo
- Follow-up
- Three months
- Study design
- Randomized double-blind placebo-controlled trial with per-protocol analysis
Only 15 active and 17 placebo participants remained in the EMG analysis, and 12 and 13 remained in the biopsy analysis; 19 per arm were excluded for compliance or loss, plus one active participant after reinnervation. No patient-function benefit was shown. The corresponding author also listed Allergan R&D; the report contains no explicit funding declaration.
Read the original sourceMaltin et al. · post-meniscectomy strength study
Randomized double-blind clinical trial
Maltin CA, Delday MI, Watson JS, et al. Clinical Science. 1993;84(6):651-654. PMID 8334811. DOI 10.1042/cs0840651.
The study reported relative recovery and a contralateral-leg within-group signal after meniscectomy; absolute strength did not differ significantly between randomized groups.
- Participants / model
- 20 healthy male patients after medial meniscectomy
- Treatment
- Clenbuterol or placebo
- Follow-up
- Four weeks plus washout
- Study design
- Randomized double-blind clinical trial
A postoperative rehabilitation result does not establish healthy strength enhancement.
Read the original sourceKamalakkannan et al. · heart-failure trial
Randomized placebo-controlled pilot trial
Kamalakkannan G, Petrilli CM, George I, et al. Journal of Heart and Lung Transplantation. 2008;27(4):457-461. PMID 18374884. DOI 10.1016/j.healun.2008.01.013.
Lean mass increased. Maximum strength rose 27% in the active arm and 14% in placebo within groups, while endurance and exercise duration fell.
- Participants / model
- 19 patients with NYHA class II to III chronic heart failure; 10 active and 9 placebo; 17 completed
- Treatment
- Clenbuterol or placebo
- Follow-up
- 12 weeks
- Study design
- Small randomized placebo-controlled pilot
Two active participants withdrew for adverse effects, and the study did not establish a clear absolute between-group strength benefit.
Read the original sourceKoeberl et al. · randomized Pompe pilot
Randomized double-blind placebo-controlled phase 1/2 trial
Koeberl DD, Case LE, Smith EC, et al. Molecular Therapy. 2018;26(9):2304-2314. PMID 30025991. DOI 10.1016/j.ymthe.2018.06.023.
At week 52 the active arm changed 6-minute walk distance by +16 m (p=.08), predicted distance +3% (p=.03), inspiratory pressure +8%, quick motor score +7 points, gait/stairs score +2 points, and vastus glycogen -50%.
- Participants / model
- 13 adults with late-onset Pompe disease on enzyme replacement; 8 active and 5 placebo; 11 completed
- Treatment
- Adjunctive clenbuterol or placebo
- Follow-up
- 52 weeks
- Study design
- Randomized double-blind placebo-controlled phase 1/2 pilot
- Funding
- Academic and disease-research support; author and institutional technology and industry interests were disclosed
Baseline groups differed markedly, the trial was underpowered, and the paper emphasized within-group change instead of direct arm comparisons.
Read the original sourceQuerin et al. · open SBMA pilot
Open-label pilot trial
Querin G, D'Ascenzo C, Peterle E, et al. Neurology. 2013;80(23):2095-2098. PMID 23645595. DOI 10.1212/WNL.0b013e318295d766.
Six-minute walk distance and forced vital capacity improved from baseline among completers; MRC and ALSFRS-R measures did not.
- Participants / model
- 20 patients with spinal and bulbar muscular atrophy; 16 completed 12 months
- Treatment
- Open-label clenbuterol
- Follow-up
- 12 months
- Study design
- Uncontrolled open-label pilot
No concurrent comparator was used, and the disease-specific result does not establish healthy performance.
Read the original sourceLi et al. · high-withdrawal ALS pilot
Open-label clinical trial
Li X, Koeberl DD, Lutz MW, Bedlack R. Journal of Clinical Neuromuscular Disease. 2023;24(4):214-221. PMID 37219865. DOI 10.1097/CND.0000000000000438.
Authors reported slower ALSFRS-R and FVC slopes during treatment, but 14/25 withdrew early and 13 withdrawals were due to adverse effects. Pretreatment slopes were back-calculated by assuming normal scores at disease onset.
- Participants / model
- 25 people with ALS
- Treatment
- Open-label clenbuterol
- Follow-up
- 24 weeks
- Study design
- Uncontrolled open-label trial using back-calculated pretreatment slopes
- Funding
- Donations from one patient's family; investigators disclosed multiple industry relationships and institutional financial interests
The design and attrition prevent a causal efficacy claim.
Read the original sourceSpiller et al. · poison-center misuse series
Poison-center case series
Spiller HA, James KJ, Scholzen S, Borys DJ. Substance Abuse. 2013;34(3):306-312. PMID 23844963. DOI 10.1080/08897077.2013.772083.
Thirteen poison-center cases were described; 11 involved bodybuilding or weight-loss intent, symptoms could persist beyond 24 hours, and two cases had myocardial injury.
- Participants / model
- 13 reported clenbuterol misuse or abuse cases
- Treatment
- Uncontrolled market-product exposure
- Follow-up
- Clinical course beyond 24 hours in some cases
- Study design
- Descriptive poison-center case series
There is no exposed-user denominator, and dose, co-use, and product identity limit attribution.
Read the original sourceBonenti et al. · Global Drug Survey comparison
Cross-sectional self-report study
Bonenti B, Puljević C, Steve V, et al. Performance Enhancement & Health. 2025;13:100356. DOI 10.1016/j.peh.2025.100356.
Among 1,146 male 2024 Global Drug Survey respondents, 197 reported AAS plus clenbuterol and 949 AAS without clenbuterol. Age-adjusted odds ratios were 2.76 for negative heart effects, 1.73 for rapid mood fluctuation, and 1.61 for irrational excitability; restlessness/irritability was 1.36 (p=.122).
- Participants / model
- 1,146 male AAS users in the 2024 Global Drug Survey
- Treatment
- Self-reported AAS plus clenbuterol versus AAS without clenbuterol
- Follow-up
- Prior 12-month use
- Study design
- Cross-sectional anonymous survey comparison
- Funding
- No specific grant
Self-selection, younger age, earlier or heavier AAS use, other substances, missing dose data, recall, and the absence of a clenbuterol-only arm prevent causal or drug-to-drug safety conclusions.
Read the original sourceClinicalTrials.gov · current clenbuterol trial status
Clinical trial registry record set
ClinicalTrials.gov listed 12 clenbuterol intervention records.
NCT06721299 was recruiting with estimated n=30 in FSHD; NCT06169046 was recruiting with estimated n=90 in SBMA; NCT05692856 had unknown status after January 2023 with estimated n=60. None had posted results.
- Participants / model
- Registered clenbuterol studies
- Treatment
- Clenbuterol in disease or muscle-study protocols
- Study design
- Exact-intervention registry coverage
- Funding
- Sponsors vary by record
A 2026 KLHL41 biomarker report appears to reuse the completed NCT03860870 cohort and is not independent clinical replication. Recent Chinese fixed ambroxol-plus-clenbuterol studies cannot isolate clenbuterol. The cited records contain no independent Russian-language administered-human enhancement result.
Read the original sourceWhy is Clenbuterol in F tier?
F reflects the healthy-use balance. The direct trial found 0.91 kg more lean mass over two weeks, with no fat-mass or sprint benefit and lower VO2max and work capacity. Controlled trials repeatedly report higher heart rate, tremor, cramps, and palpitations, while misuse reports document serious cardiovascular and metabolic toxicity.