Testosterone

A hormone and a medicine

Testosterone is an androgen hormone and a prescription medicine for diagnosed deficiency. The parent hormone, its esters and the finished formulations have different release and absorption profiles.^684,685,686

The product determines the instructions

Daily gels, injections, oral undecanoate capsules and implanted pellets have their own absorption, monitoring and safety instructions. Oral undecanoate capsules carry product-specific food and testing instructions.^{684,688,689,690,691}

Clinical benefits

Sexual desire and activity

The Testosterone Trials studied 790 men age 65 or older with low testosterone and symptoms. A year of gel improved sexual activity, desire and erectile function. In the larger TRAVERSE program, a 1,161-man sexual-function substudy found sustained gains in activity and desire, while erectile function was unchanged.^692,693

Energy, mood and memory

The Testosterone Trials found small improvements in mood and depressive symptoms. The primary fatigue measure showed no significant benefit. A separate cognitive analysis found no improvement in memory or other measured cognitive functions in men with age-associated memory impairment.^692,694

Muscle and strength

A 10-week trial randomized 43 healthy men to testosterone or placebo, with or without resistance training. Experimental supraphysiologic testosterone increased fat-free mass, muscle size and strength; the testosterone-plus-training group had the largest gains.⁶⁹⁶

Heart and bone outcomes

Bone density and fractures

A 211-person Testosterone Trials substudy found higher bone density and estimated bone strength after a year of gel. The later TRAVERSE fracture analysis followed 5,204 men for a median 3.19 years: clinical fractures occurred in 3.50% with testosterone and 2.46% with placebo. These are separate endpoints with different results.^698,699

Coronary plaque

In a Testosterone Trials imaging substudy, 138 men completed the primary analysis. Testosterone was associated with 41 mm3 more progression of noncalcified coronary plaque than placebo over 12 months. TRAVERSE later provided the larger clinical-event comparison.^700,697

Prostate outcomes

TRAVERSE excluded men with higher prostate-cancer risk and severe urinary symptoms. Adjudicated high-grade cancers and other prostate events were uncommon and did not differ significantly between groups. PSA rose more with testosterone.⁷⁰¹

The risks worth knowing

Blood pressure and hematocrit

Testosterone can raise blood pressure and red-cell mass. Product labels call for monitoring both. European safety updates also address increased hemoglobin and hematocrit when testosterone is used with SGLT2 inhibitors.^702,684,703

Gel transfer

Residue on treated skin can expose children, partners or pets. Labels describe handwashing, covering the dried application site and washing the site before anticipated skin contact. The exact product leaflet gives the application and washing instructions.^684,704,705

A product-specific injection warning

Aveed retains a boxed warning for pulmonary oil microembolism and anaphylaxis. Its US label requires observation in a healthcare setting for 30 minutes after every injection, with restricted access through a REMS program.⁶⁸⁶

Skin, hair and breast effects

Current labels include acne, male-pattern hair loss and gynecomastia. Breast enlargement can persist. The frequencies and other adverse effects depend on the product and the population studied.^685,684

Fertility and women's health

Sperm production can fall sharply

External testosterone suppresses the hormones that support sperm production. A Chinese contraception program enrolled 1,045 fertile men; 855 entered the efficacy phase and nine pregnancies occurred over 1,554.1 person-years. Two participants had not returned to the normal fertile sperm range at the end of follow-up.^706,707

A UK approval for low sexual desire

The UK authorized AndroFeme cream in July 2025 for hypoactive sexual desire disorder in postmenopausal women on optimized hormone therapy, after other treatable causes are considered. The assessment describes limited safety information beyond two years.⁷⁰⁸

Cream trial outcomes

The AndroFeme assessment includes an earlier crossover trial of 36 postmenopausal women after hysterectomy who were already using estrogen. Sexual outcomes improved during testosterone treatment; mood, energy, blood pressure, lipids and weight were unchanged. This is the same trial reported in 2007.^709,708

International studies

A Russian metabolic-syndrome trial

The Moscow study randomized 184 men with low testosterone and metabolic syndrome to testosterone undecanoate or placebo for 30 weeks. Weight, waist circumference, insulin and several inflammatory markers fell more with testosterone. Glucose and lipid measures were unchanged.⁷¹⁰

After prostate surgery

A Russian single-center study assigned 60 men with low testosterone undergoing prostate surgery to gel or no replacement. Sexual-symptom scores improved over 12 weeks, while urinary-flow and prostate-volume results were similar. The small surgical setting limits how widely the results apply.⁷¹¹

A Korean follow-up study

A Korean study followed 26 men with secondary hypogonadism for 12 months on oral undecanoate or injected enanthate. Lean mass increased; visceral fat and insulin-resistance measures showed no significant change. Most participants also received other pituitary-hormone replacements.⁷¹²

Diabetes prevention

TRAVERSE included 1,175 men with prediabetes and 3,880 with diabetes in its glucose analysis. Testosterone gel did not significantly reduce progression to diabetes or improve glycemic control.⁷¹³

Labels and sport rules

United States label changes

In 2025, FDA removed the class-wide boxed-warning language about increased cardiovascular events and required blood-pressure warnings. Its April 2026 invitation for low-libido indication applications and June 2026 labeling request are separate regulatory steps. Current wording must be checked on the individual product label.^{702,714,715,690}

Competitive sport

WADA's 2026 and 2027 lists prohibit externally administered testosterone and its esters at all times. Athletes using prescribed testosterone need the therapeutic-use-exemption rules for their sport and circumstances.^716,717,718

Common questions

The questions readers ask, answered from the studies.

01 How do injections, gels, oral capsules and pellets differ?

Injections, gels, oral capsules and pellets are distinct products with route-specific instructions. Gels are applied daily and can transfer by skin contact; injections and pellets have product-specific release profiles; oral testosterone undecanoate has formulation-specific food and testing instructions. Each result applies to the ester, vehicle, route and monitoring point studied.^{684,719,686,688,691}

02 How long do testosterone esters and products stay in the body?

There is no single testosterone half-life. Two phase 1 cohorts totaling 21 hypogonadal men produced estimates of 33.9 days for a castor-oil undecanoate preparation and 20.9 days for a tea-seed-oil preparation; the current Depo-Testosterone label reports about eight days for cypionate. The Xyosted label gives peak timing and steady state but no elimination half-life.^685,720,719

03 What evidence exists for testosterone use in women?

Evidence and authorization depend on the product and population. The UK authorized AndroFeme cream in 2025 for hypoactive sexual desire disorder in postmenopausal women on optimized hormone therapy after other treatable causes are considered; its assessment notes limited safety information beyond two years. A Brazilian registry result used a compounded gel with background hormone therapy, so it describes a different product and setting.^708,721,722

04 How is low testosterone diagnosed?

Low testosterone is diagnosed from compatible symptoms plus more than one consistently low measurement. The Endocrine Society guideline calls for a repeat morning fasting measurement and investigation of the cause, with LH and FSH helping distinguish testicular from brain-pituitary causes.⁶⁸⁷

05 Does testosterone build muscle or improve performance?

In a 10-week trial of 43 healthy men, supraphysiologic testosterone enanthate increased fat-free mass, muscle size and strength, with the largest gains in the testosterone-plus-training group.⁶⁹⁶

06 Why are hematocrit and blood pressure monitored?

Testosterone can increase red-cell mass and blood pressure, so labels call for hematocrit and blood-pressure checks. European regulators also added an interaction warning because SGLT2 inhibitors and testosterone can both raise hemoglobin and hematocrit. The exact testing schedule depends on the product and clinical setting.^684,702,703

07 Can testosterone improve mood, energy or brain fog?

Average effects on mood and energy were modest. In the Testosterone Trials, the primary vitality result was not significant, while mood and depressive symptoms improved slightly; trials measured specific mood and vitality scales rather than one standard brain-fog outcome.^692,723

08 How much does testosterone therapy cost, and are generics available?

There is no single price for testosterone therapy. Cost and availability vary by formulation, strength, insurance and country; FDA records include approved brand and generic applications, but a generic injection, gel, oral capsule or pellet is not an interchangeable substitute for another form.⁷²⁴

09 Does testosterone lower sperm count or fertility?

External testosterone suppresses the hormones that support sperm production, and sperm counts can fall to zero. In a monitored Chinese contraception program, 1,045 fertile men enrolled and 855 entered the efficacy phase. Over 1,554.1 person-years, nine pregnancies occurred despite the monitored suppression regimen.^706,725,707

10 Can testosterone cause hair loss, acne or breast changes?

Yes. Current labels list acne, male-pattern baldness and gynecomastia, and gynecomastia can persist. Labels do not give one universal frequency across products.^685,684

11 What do studies show about heart attack, stroke and clot risk?

TRAVERSE enrolled 5,246 men with hypogonadism and existing or high cardiovascular risk who used testosterone gel or placebo. Major cardiovascular events were 7.0% versus 7.3% (HR 0.96), meeting the trial's noninferiority criterion, while atrial fibrillation, acute kidney injury and pulmonary embolism occurred more often with testosterone.^697,684

12 How can testosterone gel transfer to other people or pets?

Transfer can occur when another person or pet touches residue on the application site. Use the instructions for the exact gel: wash your hands, let the site dry, cover it with clothing, and wash the site before expected skin contact. Current UK and EU warnings specifically address children and pets.^684,704,705

13 How long does testosterone take to work?

Replacement trials measured changes over months rather than days. In the TRAVERSE sexual-function substudy, benefits in sexual activity and desire were present at the six-month assessment and followed through two years.⁶⁹³

14 Does testosterone change weight or body fat?

In a 30-week randomized trial of 184 men with low testosterone and metabolic syndrome, testosterone produced greater reductions in weight and waist circumference, while glucose and lipid measures did not improve.^710,692

15 Can testosterone improve libido or erections?

Replacement can improve sexual desire and activity in men with confirmed low testosterone. The Testosterone Trials found a modest erectile-function benefit, while the larger TRAVERSE sexual-function substudy improved sexual activity and desire but not erectile function.^692,693