testosterone

the male sex hormone. the approved products replace it in men whose own production has failed, and above that range the same molecule adds muscle and strength with no training at all. schedule iii controlled substance in the us. educational record only, not medical advice.

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

verdict

the male sex hormone. the approved products replace it in men whose own production has failed, and above that range the same molecule adds muscle and strength with no training at all. it is the most-studied compound on the board. of the seven ester half-lives everyone quotes, two trace back to a measurement in humans.

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 ride along under the chapeau clause covering salts, esters and ethers, so one line of text schedules the whole family. everything below is an educational record of what published trials and FDA label text contain. it is not a protocol, and decisions about hormone therapy belong with a licensed physician.

for anyone asking which ester and why: the ester is a chain bolted onto the hormone, and its length decides how fast the oil lets the hormone go. the gap between administrations, the swing between peak and trough, and the volume of oil all follow from that. a short ester given weekly runs flatter than a long ester given every ten weeks. cypionate carries 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 clears in 10 to 100 minutes, so in oil it gives a spike and then nothing.

for anyone asking whether it damages the heart: at replacement targets the largest trial says no. TRAVERSE followed 5,246 men and put the hazard ratio for major cardiac events at 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. it ran on a transdermal gel in men with mild to moderate deficiency, so it covers replacement and stops there. at the far larger exposures reported outside clinics the evidence is two cross-sectional studies, and both find reduced ejection fraction that persists years after cessation.

for anyone arriving through the grey market: the odds that a grey-market vial holds what its label claims are poor, and worse for oil than for tablets. 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% contained something other than 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 a wider margin than anything else on the 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. A-tier is for a strong mechanism with a missing approval, and testosterone has the approval. The grade measures the evidence and stops there. It says nothing about whether anyone should research the compound, about supraphysiologic exposure, or about any way of obtaining it, and this is the only S-tier entry that is also a federally controlled substance carrying the worst analytical record on the board.

the core tension

Testosterone has the deepest evidence base on the 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 holds two sourceable numbers, and the other five stay in circulation because people keep copying them.

what it is

Testosterone is the male sex hormone. A man's own body makes it, and every product here puts that same molecule into the blood from outside. Chemically it is a 19-carbon steroid, the principal endogenous androgen, which makes it the odd one out on a board of peptides. In the United States it is a Schedule III controlled substance listed at 21 CFR 1308.13(f). Plain testosterone is a poor drug by every route. Swallowed, the liver destroys most of it before it can work. Injected on its own it clears almost immediately, and the AVEED label puts the reported half-life at 10 to 100 minutes. So almost every injected product is an ester instead: a fatty chain bolted onto the hormone (at the 17-beta hydroxyl) that keeps it dissolved in oil and lets it out slowly, until enzymes in tissue snip the chain off and plain testosterone is what circulates. Seven chains are sold: propionate, phenylpropionate, isocaproate, enanthate, cypionate, decanoate and undecanoate. All seven deliver the same hormone to the same receptor, and all seven leave the oil at a different speed.

what it does

It raises the amount of the hormone in the blood. In men whose own concentration has fallen, the approved products bring it back into a normal range, and above that range the same molecule adds muscle and strength with no training at all. 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. One problem shaped everything that came after, and Nieschlag's history states it plainly. Swallowed, testosterone is inactivated in the liver, so the field had to find injected routes or change the molecule. 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 measured against it, and it is the only entry 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 the argument runs on a table of numbers that mostly cannot be traced to a source.

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. Underneath that sits a thin ester literature. Two of the seven half-lives in the standard chart have a primary human source.

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 human primary source
• 8 days cypionate t½, fda label
• 65.2% of seized oil solutions counterfeit

frequently asked questions

What is testosterone?

Testosterone is the male sex hormone. A man's own body makes it, and every product here supplies the same molecule from outside. The US labels approve it as replacement in men with hypogonadism, meaning the body's own production has failed, and every US label reviewed here adds that use in men with age-related hypogonadism has not been established. The market names it by its ester, testosterone enanthate or testosterone cypionate, and the brand names are Depo-Testosterone, XYOSTED, AVEED, TESTOPEL, JATENZO and KYZATREX in the United States, Nebido and the four-ester blend Sustanon in Europe. Federal law calls it an anabolic steroid. Chemically it is the principal endogenous androgen, a 19-carbon steroid, which makes it the odd one out on a board of peptides. 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 injected products carry an ester, a fatty chain bolted onto the hormone, because the AVEED label puts the circulating half-life of the bare hormone at 10 to 100 minutes.

What does testosterone do?

It raises the amount of that hormone in the blood. In men with hypogonadism, meaning their own concentration is low, the approved products restore it, and above that range it adds muscle mass and strength independent of training. Administered testosterone also shuts down the body's own production and suppresses sperm production, which in the 2018 cypionate study was complete by 14 weeks at 250 and 500 mg weekly and had not fully recovered by week 40 in some men. 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 how fast the oil releases the hormone, and the gap between administrations, the swing between peak and trough and the volume of oil all follow from that.

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 covered by the chapeau clause on salts, esters and ethers, so one line of text schedules the whole family. 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 predicted polycythemia, while the duration of therapy carried no signal at all. 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 chain is greasier, holds on to the oil longer, and buys a longer gap between administrations. A shorter chain releases faster, peaks higher and earlier, and has to be given more often. Longer chains also carry more dead weight per milligram: the Nebido SmPC states that 250 mg of testosterone undecanoate corresponds to 157.9 mg of testosterone. Stretching the interval widens the swing between peak and trough, so a long ester given rarely runs bumpier than a short ester given weekly. Two of the seven ester half-lives in the standard chart have a traceable primary human 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. Enanthate's widely quoted 4.5 days was asserted in a 1995 paper, and the only measurement of it anywhere is 4 to 5 days in macaques.

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.