testosterone

schedule iii controlled substance in the us. educational record only, not medical advice.

tier S · libido · 5,246 TRAVERSE · HR 0.96

verdict

the most-studied molecule on the board, and an ester chart where five of the seven half-lives have no primary source behind them.

for anyone asking whether any of this is advice — it is not. testosterone is a schedule iii controlled substance in the united states, listed at 21 CFR 1308.13(f), and the esters are scheduled with it through the chapeau clause covering salts, esters and ethers rather than through lines of their own. everything below is an educational record of what published trials and FDA label text contain, not a protocol and not a substitute for a licensed physician.

for anyone asking which ester and why — the chain length sets how fast the oil gives the molecule up, and interval, peak-to-trough swing and volume all follow from it. a short ester given weekly is flatter than a long ester given every ten weeks. cypionate has the only label-stated half-life, roughly eight days. undecanoate buys a ten-week interval and pays for it with 3 to 4 mL of oil and a boxed warning for pulmonary oil microembolism. the unesterified base is not an oil depot at all, because it clears in 10 to 100 minutes.

for anyone asking whether it damages the heart — at replacement targets, TRAVERSE says no on the primary endpoint: 5,246 men, hazard ratio 0.96, 95% CI 0.78 to 1.17. the same trial recorded a higher incidence of atrial fibrillation, acute kidney injury and pulmonary embolism. that trial ran on a transdermal gel in men with mild to moderate deficiency, and it says nothing about supraphysiologic exposure, where two cross-sectional studies find reduced ejection fraction that persists years after cessation.

for anyone arriving through the grey market — a 19-study meta-analysis of 5,413 samples found 36% counterfeit and 37% substandard, with counterfeit proportions of 43 to 65% for oil-based solutions against 29 to 37% for tablets. a brazilian police analysis put 65.2% of oil solutions counterfeit against 28.7% of tablets. a 2025 swiss pilot testing material submitted by the people who intended to administer it found 52% was not what the label said.

schedule iii controlled substance. educational reference built from published trials and FDA label text, not medical advice and not a dosing protocol.

why S-tier

S-tier because the bar for S is drug-grade human evidence and testosterone clears it by more than anything else on this board: FDA-approved products across six routes, a 5,246-participant randomised cardiovascular outcomes trial, an Endocrine Society guideline built on two commissioned systematic reviews, and ninety years of clinical use. Not A, because A is for compounds with a strong mechanism and a missing approval. The grade is a statement about the evidence and nothing else. It is not an endorsement of the compound, of supraphysiologic exposure, or of any way of obtaining it, and this is the only S-tier entry here that is also a federally controlled substance with the worst analytical record on the board.

the core tension

Testosterone has the deepest evidence base of anything on this board and the shallowest ester literature of anything the market argues about this confidently. The trial that earns the grade ran on a transdermal gel, in men with mild to moderate deficiency, at replacement targets, for a mean of 21.7 months on drug. The chart the market uses to choose between propionate, enanthate, cypionate and undecanoate has two sourceable numbers in it and five that repeat without a measurement behind them.

what it is

Testosterone is the principal endogenous androgen, a 19-carbon steroid hormone, and in the United States a Schedule III controlled substance listed at 21 CFR 1308.13(f). It is not a peptide. Given raw it is a poor drug in every route. Taken by mouth it is inactivated in the liver. Injected on its own it disappears: the AVEED label states that reported half-lives for unesterified testosterone range from 10 to 100 minutes. Almost every parenteral testosterone product is therefore an ester, an acyl chain attached at the 17-beta hydroxyl that slows release from an oil depot until tissue esterases cleave it back to free testosterone. The commercial esters are propionate, phenylpropionate, isocaproate, enanthate, cypionate, decanoate and undecanoate. Identical at the receptor, and seven different release curves out of the oil.

what it does

Restores circulating androgen concentration, and at supraphysiologic exposure adds muscle mass and strength independent of training. TRAVERSE, the largest cardiovascular outcomes trial on the molecule, randomised 5,246 hypogonadal men with high cardiovascular risk to a daily 1.62% gel titrated to 350 to 750 ng/dL. Major adverse cardiac events were 7.0% against 7.3% on placebo, hazard ratio 0.96, 95% CI 0.78 to 1.17. Atrial fibrillation, acute kidney injury and pulmonary embolism were each more common in the testosterone group. Bhasin's 1996 trial gave 43 eugonadal men 600 mg of enanthate weekly for 10 weeks. Without any exercise, triceps area rose 424 mm2 (SE 104) against a fall of 81 on placebo, and bench press rose 9 kg (SE 4).

origin

Isolated by Ernst Laqueur in Amsterdam and synthesised by Adolf Butenandt and Leopold Ruzicka in 1935. Nieschlag's history of the molecule states the design constraint that produced everything after: given orally, testosterone is inactivated in the liver, so parenteral routes or modifications of the molecule had to be found. Eighty-five years of preparation development followed, aimed at a formulation that reaches physiological serum concentrations.

why researchers are interested

It is the reference compound. Every androgen conversation on the board is calibrated against it, and it is the only entry here with FDA-approved products across intramuscular, subcutaneous, oral, transdermal, nasal and implanted routes. The ester question is the part the market actually argues about, and it is argued with a table of numbers that mostly cannot be traced.

does it work

Yes, in the sense the tier board means. Multiple approved products, a 5,246-participant randomised outcomes trial, an Endocrine Society guideline, ninety years of clinical use. The qualifications matter more here than on any other S-tier entry. TRAVERSE ran on a gel, in men with symptoms and two confirmed measurements below 300 ng/dL, excluding those below 100, at replacement targets, and roughly a third of its follow-up was off drug. The ester literature underneath is thin enough that five of the seven half-lives in the standard chart have no primary source.

claims vs the data

• testosterone therapy raises the risk of heart attack and stroke — contradicted — TRAVERSE, n=5,246, HR 0.96 (95% CI 0.78-1.17) for MACE. gel, replacement targets, and men below 100 ng/dL were excluded. the same trial found more atrial fibrillation, acute kidney injury and pulmonary embolism.
• supraphysiologic doses build muscle without training — supported — Bhasin 1996, 600mg enanthate weekly, 10 weeks, no exercise: triceps +424 mm2 (SE 104), bench +9 kg (SE 4) vs placebo losses. n=43.
• the standard ester half-life chart is established fact — unverified — two of seven traceable. cypionate ~8 days (label), undecanoate 33.9 d (Behre, n=14). enanthate and propionate reach peer-reviewed text only as a secondary citation inside another paper's discussion, and phenylpropionate, isocaproate and decanoate have no indexed source at all.
• a longer ester gives smoother blood levels — partially true — the interval sets the swing, not the ester alone. weekly subcutaneous enanthate runs ~790/436 ng/dL peak to trough; undecanoate on a 10-week interval runs ~37/16 nmol/L. the short ester is flatter.
• undecanoate's ten-week interval is a free upgrade — contradicted — it requires 3 to 4 mL of oil. boxed warning for pulmonary oil microembolism and anaphylaxis, 30-minute observation, REMS. Australian prospective data: 19 POME events per 1,000 injections (95% CI 14-24).
• oral and intramuscular undecanoate are the same drug — contradicted — same molecule, unrelated numbers. ~150 minutes oral vs 21-34 days intramuscular; Tmax 2-4 hours vs ~7 days; twice-daily with food, and exposure moves with meal fat content.
• cardiac changes from long-term use reverse after stopping — contradicted — Abdullah 2024: ejection fraction at or below 40% in 11% of current and 10% of former users, not significantly different, with former users a mean 6 years off. cross-sectional, n=101 users vs 71 controls.
• grey-market vials contain what the label says — contradicted — 36% counterfeit and 37% substandard across 19 studies and 5,413 samples; 65.2% of seized oil solutions counterfeit in the Brazilian analysis; 52% of user-submitted samples wrong in the 2025 Swiss pilot.
• hematocrit rise is a problem of the long esters only — contradicted — 2025 systematic review of 18 studies: every formulation raised it, up to 5% on undecanoate and up to 6.9% on intermediate-acting esters. trough concentration predicts polycythemia, not duration of therapy.
• propionate hurts more than the longer esters — unverified — no primary source located. no single-ester propionate US label exists and no indexed human comparison of site reactions across testosterone esters turned up. plausible mechanism, no measurement.

key facts

• molecular formula: C19H28O2 (base); C27H40O3 (cypionate); C26H40O3 (enanthate); C30H48O3 (undecanoate)
• molecular weight: 288.4 g/mol (base); 412.61 g/mol (cypionate); 400.59 g/mol (enanthate); 456.7 g/mol (undecanoate)
• amino acids: n/a (19-carbon steroid, not a peptide)
• half-life: ~8 days (cypionate IM, per label); 33.9 d (undecanoate in castor oil, n=14); 10-100 min (unesterified)
• type: endogenous androgen · schedule III
• CAS: 58-22-0 (base)
• 5,246 men in traverse
• 2 of 7 ester half-lives with a primary source
• 8 days cypionate t½, fda label
• 65.2% of seized oil solutions counterfeit

frequently asked questions

What is testosterone?

Testosterone is the principal endogenous androgen, a 19-carbon steroid hormone, and not a peptide. In the United States it is a Schedule III controlled substance listed at 21 CFR 1308.13(f). FDA-approved products exist as oil solutions for intramuscular administration, a weekly subcutaneous autoinjector, oral capsules, transdermal and nasal gels, and implanted pellets. Most parenteral products contain an ester rather than the free hormone, because the AVEED label puts the circulating half-life of unesterified testosterone at 10 to 100 minutes.

What does testosterone do?

It restores circulating androgen concentration in men with hypogonadism, and at supraphysiologic exposure it adds muscle mass and strength independent of training. TRAVERSE randomised 5,246 hypogonadal men with high cardiovascular risk to a 1.62% gel or placebo and found major adverse cardiac events of 7.0% against 7.3%, hazard ratio 0.96, 95% CI 0.78 to 1.17, with a higher incidence of atrial fibrillation, acute kidney injury and pulmonary embolism in the testosterone group. Bhasin's 1996 trial of 600 mg of enanthate weekly for 10 weeks in 43 eugonadal men produced measurable gains in muscle area and strength with no exercise at all.

How is testosterone typically administered?

In the approved literature, as an ester in oil given intramuscularly (cypionate at two-to-four-week intervals per its label, undecanoate at 750 mg every 10 weeks), as a weekly subcutaneous enanthate autoinjector, as oral undecanoate capsules taken twice daily with food, as a daily transdermal gel, as a nasal gel, or as crystalline pellets implanted every three to six months. The ester sets the release rate from the oil depot, and with it the interval, the peak-to-trough swing and the volume administered.

Is testosterone FDA approved?

Yes, across multiple products and routes, and it is simultaneously a Schedule III controlled substance under 21 CFR 1308.13(f), where the esters are scheduled through the chapeau clause covering salts, esters and ethers rather than by individual listing. Labelling changed in 2025: the boxed warning on blood pressure increases was removed from XYOSTED in March 2025 and from JATENZO and KYZATREX in July 2025, while AVEED's boxed warning for pulmonary oil microembolism and anaphylaxis remains in force with a 30-minute observation requirement and REMS restriction. Every US label reviewed here carries a limitation stating that use in men with age-related hypogonadism has not been established.

What are the side effects of testosterone?

Across formats, the two consistent effects are a rise in hematocrit and a rise in blood pressure. A 2025 systematic review of 18 studies found hematocrit rose up to 5% on injected undecanoate and up to 6.9% on intermediate-acting esters, with every formulation raising it; a pellet cohort of 158 men found the trough concentration, not the duration of therapy, predicted polycythemia. Ambulatory monitoring found 24-hour systolic pressure rising 1.9 mm Hg on gel, with the confidence interval crossing the prespecified margin. Product labels report 1.7 to 4.9 mm Hg systolic increases depending on the product. Long-interval undecanoate carries a boxed warning for pulmonary oil microembolism and anaphylaxis. At supraphysiologic exposure, two cross-sectional studies of long-term users found reduced left ventricular ejection fraction, in one of them equally common in current and former users a mean of six years after stopping. Spermatogenic suppression was complete by 14 weeks at 250 and 500 mg weekly and had not fully recovered by week 40 in some men.

What is the difference between the testosterone esters?

Chain length, and everything that follows from it. A longer acyl chain is more lipophilic, leaves the oil depot more slowly, and permits a longer interval; a shorter chain releases faster, peaks higher and earlier, and needs more frequent administration. Longer chains also carry more ester mass per milligram of hormone: the Nebido SmPC states that 250 mg of testosterone undecanoate corresponds to 157.9 mg of testosterone. A longer interval does not produce a flatter curve on its own, because the swing between peak and trough grows with the interval. Only two of the seven ester half-lives in the standard chart have a traceable primary source: cypionate at approximately eight days from its FDA label, and undecanoate at 33.9 days in castor oil from a 21-man phase I study in 1999.

related peptides

• hcg — the LH-analog route, used where suppression is the problem
• gonadorelin — the GnRH pulse upstream of the axis testosterone shuts down
• kisspeptin-10 — one step further up the same axis
• pt-141 — sexual-function route that never touches the androgen axis

reptides grades the research record and cites the literature behind every call. research reference only; not medical advice.