Testosterone decanoate is testosterone with a 10-carbon fatty acid (decanoic acid) attached as an ester. Like other testosterone esters, it is an inactive carrier form: after an intramuscular injection in oil, it leaves the depot slowly and is then cut back to ordinary testosterone. Its long, fat-soluble side chain is what sets it apart from shorter esters such as propionate or enanthate.
Testosterone decanoate is best known as the longest-acting of the four esters in Sustanon 250, a UK-licensed testosterone replacement product. It is not sold as a standalone finished medicine in the US. On its own, it has been studied mainly in European male hormonal contraception trials in the early 2000s, always combined with a progestin.
This page summarizes what the Sustanon 250 label, the clinical trials and regulators report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Drug class | Androgen; anabolic-androgenic steroid (testosterone ester) |
| Licensed product | Component of Sustanon 250 (UK): 100 mg of the 250 mg of esters per 1 mL ampoule |
| Route | Deep intramuscular injection (oil solution) |
| Doses studied alone | 400 mg every 4 or 6 weeks, or 600 mg every 6 weeks, in contraception trials (with a progestin) |
| Testosterone content | ≈65% of the ester’s weight (100 mg ester ≈ 65 mg testosterone) |
| Half-life | No ester-specific human half-life published that we could verify; trials dosed it every 4–6 weeks |
| US status | No FDA-approved product; testosterone esters are Schedule III controlled substances |
| WADA status | Prohibited at all times (S1.1 anabolic androgenic steroids) |
What it is
Testosterone decanoate is the 17β-decanoate ester of testosterone, formula C₂₉H₄₆O₃, molecular weight 442.7 g/mol (PubChem). Testosterone itself weighs 288.4 g/mol, so about 65% of each milligram of the ester is testosterone. The decanoate group has no hormonal activity. The Sustanon 250 label states that its esters are hydrolyzed to the natural hormone as soon as they enter the general circulation (UK SmPC).
Once released, the hormone is the same testosterone delivered by cypionate or enanthate. It acts on the androgen receptor directly and is converted in part to dihydrotestosterone (DHT) and estradiol. What differs between esters is how much testosterone each milligram contains and how fat-soluble the molecule is.
| Ester | Molecular weight | Share that is testosterone | XLogP3 (computed fat solubility) |
|---|---|---|---|
| Testosterone (no ester) | 288.4 g/mol | 100% | 3.3 |
| Propionate | 344.5 g/mol | ≈84% | 4.4 |
| Isocaproate | 386.6 g/mol | ≈75% | 5.5 |
| Enanthate | 400.6 g/mol | ≈72% | 6.3 |
| Cypionate | 412.6 g/mol | ≈70% | 6.4 |
| Phenylpropionate | 420.6 g/mol | ≈69% | 5.8 |
| Decanoate | 442.7 g/mol | ≈65% | 8.0 |
| Undecanoate | 456.7 g/mol | ≈63% | 8.5 |
Molecular weights and XLogP3 values from PubChem; testosterone share calculated as 288.4 divided by the ester’s weight.
XLogP3 is a computer-estimated measure of how strongly a molecule prefers fat over water; each whole number is roughly a tenfold difference. Decanoate sits near the top of the range, close to undecanoate, the ester used in the long-acting Nebido injection (Forsdahl et al., Drug Test Anal 2015). The same decanoate ester is used for nandrolone in Deca-Durabolin.
How it behaves in the body
Why the ester matters
A human study of oil depots, using nandrolone decanoate rather than testosterone decanoate, concluded that how fast a drug is absorbed from the oil is related to the logP (fat solubility) of the dissolved prodrug. Tissue factors such as lymph flow also play a part (Kalicharan et al., Eur J Pharm Sci 2016). This is the basis for using a long, fat-soluble ester like decanoate as the slow-release part of a blend.
Kinetics when given alone
No study we found reports a terminal half-life for testosterone decanoate alone in people. The best human data come from a contraception study in 20 healthy Chinese men given 400 mg intramuscularly every 4 weeks, together with two etonogestrel (progestin) implants (Anderson et al., Contraception 2002):
- trough (pre-injection) testosterone rose with repeated injections;
- the peak one week after the fourth injection was 31 ± 2 nmol/L (≈890 ng/dL);
- peaks rose briefly into the supraphysiologic (above-normal) range.
The authors concluded that this preparation had better kinetics than earlier injectable testosterone products. In the two larger trials that followed, peak testosterone stayed within the normal range in every group (Hay et al., JCEM 2005; Brady et al., Hum Reprod 2006). Trough levels were the weak point:
| Regimen | Trough testosterone |
|---|---|
| 400 mg every 4 weeks (Hay 2005) | Rose into the normal range |
| 400 mg every 6 weeks (Hay 2005) | Stayed just below normal |
| All three regimens (Brady 2006) | Below normal at first, rising into the normal range during treatment |
A 6-week interval at 400 mg was therefore too long to keep testosterone in the normal range throughout. These trials used a progestin as well, which also suppresses the testes, so the levels reflect almost entirely the injected testosterone.
Within Sustanon 250
In Sustanon 250, the 100 mg of decanoate delivers ≈65 mg of the product’s 176 mg of testosterone. The label reports the blend as a whole: a peak of about 70 nmol/L at 24–48 hours, with testosterone falling to the lower limit of normal in about 21 days (UK SmPC). In blood studies after a single Sustanon 250 injection, the individual intact esters peaked within 24–72 hours, with timing that varied between people and with the length of the ester side chain (Forsdahl et al., Drug Test Anal 2015, as summarized in Solheim et al., Front Physiol 2020).
Medical use and regulatory status
- UK. Testosterone decanoate is licensed as one of four esters in Sustanon 250, authorized since February 28, 1973, for testosterone replacement in men with confirmed hypogonadism and as supportive therapy for transgender men. The usual adult dose is 1 mL every 3 weeks (UK SmPC). See the Sustanon 250 page for the product’s full profile.
- US. The FDA’s approved-drug database (Drugs@FDA) lists no product containing testosterone decanoate (openFDA Drugs@FDA). The FDA’s National Drug Code directory lists it only as a bulk ingredient powder, not as a finished drug (openFDA NDC).
- US controlled-substance status. Testosterone, including its salts, esters and ethers, is a Schedule III anabolic steroid (21 CFR 1308.13).
- Sport. Testosterone and its esters are prohibited at all times, in and out of competition, under S1.1 of the WADA 2026 Prohibited List. They are non-specified substances.
What the research shows
Male hormonal contraception
Testosterone decanoate’s only substantial clinical program as a single ester tested it as the androgen half of a male contraceptive. The progestin etonogestrel suppressed the pituitary signals LH and FSH, which shuts down sperm production, while testosterone decanoate replaced the testosterone the testes stopped making.
| Study | Design and size | Regimen | Main result |
|---|---|---|---|
| Anderson et al. 2002 | Open study, 20 men | TD 400 mg every 4 weeks + 2 etonogestrel implants | All men at or under 1 million sperm/mL; 80% azoospermic (no sperm) at 12 weeks |
| Hay et al. 2005 | Randomized, 112 men, 48 weeks | TD 400 mg every 4 weeks (n = 55) or 6 weeks (n = 57) + oral etonogestrel 300 µg daily | At week 48, all men except one (6-week group) under 1 million/mL; faster suppression with 4-weekly dosing |
| Brady et al. 2006 | Randomized, 130 men, 48 weeks | 2 etonogestrel implants + TD 400 mg every 4 weeks (n = 42), 400 mg every 6 weeks (n = 51) or 600 mg every 6 weeks (n = 37) | Under 1 million/mL by week 24 in 90%, 82% and 89% |
TD, testosterone decanoate.
A Cochrane review reported azoospermia rates of 95% (4-weekly) and 83% (6-weekly) in the Hay trial, and 78–85% across the groups of the Brady trial (Grimes et al., Cochrane 2012). It rated these two trials among the few in the field large enough for the percentages to be meaningful. Brady and colleagues attributed the weaker results with 400 mg every 6 weeks to an inadequate testosterone dose.
Sperm counts and gonadotropins recovered to normal after treatment stopped in the Hay trial. No testosterone decanoate contraceptive reached the market.
Breast cancer (historical)
Androgens were once used to treat advanced breast cancer. A 1975 randomized study compared testosterone decanoate, drostanolone and testolactone in metastatic breast cancer (Rieche and Wolff, Arch Geschwulstforsch 1975). The authors reported similar response rates with each hormone alone, and higher objective response rates (46–55% vs 22–25%) when cyclophosphamide chemotherapy was added. The available abstract gives no patient numbers, and this use has long been abandoned.
Muscle and performance
There are no controlled human trials of testosterone decanoate alone on muscle size, strength or performance. The dose-response data for testosterone come from enanthate, summarized on the testosterone cypionate page. Because the released hormone is identical, those results apply in terms of the testosterone dose, not the ester.
In male rats given 15 mg/kg every third day for 24 days, testosterone decanoate did not impair recognition memory, while nandrolone decanoate did (Zelleroth et al., Horm Behav 2024). This is animal data and cannot be applied directly to people.
Side effects and risks
In the contraception trials
These men also received a progestin, so the findings cannot be attributed to testosterone decanoate alone.
- Blood counts. In the 20-man study, hemoglobin rose by 9% and hematocrit (the share of blood made up of red cells) by 15%. Weight also increased (Anderson et al., Contraception 2002). Mean hemoglobin rose in the 4-weekly group of the Brady trial.
- Liver tests. The 20-man study was stopped after 12–18 weeks because some men had elevated liver enzyme tests.
- Lipids and weight. The Brady trial found a non-significant fall in HDL (“good”) cholesterol and rise in weight in all groups. The Hay trial noted minor effects on weight and cholesterol.
- Withdrawals. Fourteen men withdrew because of adverse events in each of the two large trials. In the Hay trial, events possibly related to the drugs were more common in the 6-weekly group (9 vs 1).
Labeled risks as part of Sustanon 250
The Sustanon 250 label lists the reactions of androgen therapy in general (UK SmPC):
- Common: weight gain; raised hematocrit, hemoglobin and red cell count.
- Rare: pulmonary oil microembolism (oil reaching the lungs during or right after injection, causing cough, breathlessness or fainting).
- Frequency not known: polycythemia, fluid retention, high blood pressure, mood changes, acne, gynecomastia, low sperm count, priapism, prostate growth, raised PSA, abnormal liver tests and lipid changes.
The label warns that side effects cannot be reversed quickly by stopping, because the depot keeps releasing hormone. This matters most for the longest-acting component, which is the decanoate. The label also notes that testosterone abuse, usually at high doses and with other steroids, has caused serious cardiovascular, liver and psychiatric events, some fatal, and can lead to dependence.
Fertility
External testosterone suppresses LH and FSH and, with them, sperm production. The contraception trials above show how strong this effect is when testosterone decanoate is combined with a progestin. The Sustanon 250 label lists oligospermia (low sperm count) and warns that androgens can impair male fertility.
Who should not use it
The Sustanon 250 label contraindicates it in:
- pregnancy and breastfeeding;
- known or suspected prostate or breast cancer;
- allergy to any ingredient, including peanut (arachis) oil, and in people allergic to peanuts or soya.
Detection in sport
Finding an intact testosterone ester in blood proves the testosterone came from outside the body (Forsdahl et al., Drug Test Anal 2015). After two Sustanon 250 injections in 9 men, a dried blood spot method detected testosterone decanoate along with the other three esters. The product was detectable in all subjects for at least 5 days, and up to 14 days for three of the esters (Solheim et al., Drug Test Anal 2022).
Key takeaways
- A long ester of ordinary testosterone. About 65% of its weight is testosterone, and the decanoate chain makes it one of the most fat-soluble testosterone esters.
- Mainly a blend component. Its licensed use is as the 100 mg slow-release part of Sustanon 250 in the UK. There is no FDA-approved product, and it is Schedule III in the US.
- No verified half-life. No published human study we found reports a terminal half-life for this ester alone.
- Studied as a male contraceptive. With etonogestrel, 400 mg every 4 weeks suppressed sperm production in most men and kept testosterone in the normal range; every 6 weeks was too long.
- Same risks as other testosterone. Raised hematocrit, suppressed fertility and lipid changes are expected, and its long action means effects do not stop quickly.
Sources
- Aspen Pharma Trading Limited. Sustanon 250, 250mg/ml solution for injection: Summary of Product Characteristics. PL 39699/0059; revised December 2025. emc.
- National Center for Biotechnology Information. PubChem compound summaries: testosterone decanoate (CID 155143), testosterone (CID 6013), propionate (CID 5995), isocaproate (CID 231084), enanthate (CID 9416), cypionate (CID 441404), phenylpropionate (CID 14743), undecanoate (CID 65157). PubChem.
- Kalicharan RW, Schot P, Vromans H. Fundamental understanding of drug absorption from a parenteral oil depot. Eur J Pharm Sci. 2016;83:19–27. PubMed.
- Anderson RA, Zhu H, Cheng L, Baird DT. Investigation of a novel preparation of testosterone decanoate in men: pharmacokinetics and spermatogenic suppression with etonogestrel implants. Contraception. 2002;66(5):357–364. PubMed.
- Hay CJ, Brady BM, Zitzmann M, et al. A multicenter phase IIb study of a novel combination of intramuscular androgen (testosterone decanoate) and oral progestogen (etonogestrel) for male hormonal contraception. J Clin Endocrinol Metab. 2005;90(4):2042–2049. PubMed.
- Brady BM, Amory JK, Perheentupa A, et al. A multicentre study investigating subcutaneous etonogestrel implants with injectable testosterone decanoate as a potential long-acting male contraceptive. Hum Reprod. 2006;21(1):285–294. PubMed.
- Grimes DA, Lopez LM, Gallo MF, Halpern V, Nanda K, Schulz KF. Steroid hormones for contraception in men. Cochrane Database Syst Rev. 2012;(3):CD004316. PubMed; PMC.
- Rieche K, Wolff G. Comparison of testosterone decanoate, drostanolone and testololactone in disseminated breast cancer: a randomized clinical study. Arch Geschwulstforsch. 1975;45(5):485–488. PubMed.
- Forsdahl G, Erceg D, Geisendorfer T, et al. Detection of testosterone esters in blood. Drug Test Anal. 2015;7(11-12):983–989. PubMed.
- Solheim SA, Mørkeberg J, Juul A, et al. An intramuscular injection of mixed testosterone esters does not acutely enhance strength and power in recreationally active young men. Front Physiol. 2020;11:563620. PubMed.
- Solheim SA, Levernaes MCS, Mørkeberg J, et al. Stability and detectability of testosterone esters in dried blood spots after intramuscular injections. Drug Test Anal. 2022;14(11-12):1926–1937. PubMed.
- Zelleroth S, Stam F, Nylander E, et al. The decanoate esters of nandrolone, testosterone, and trenbolone induce steroid specific memory impairment and somatic effects in the male rat. Horm Behav. 2024;161:105501. PubMed.
- US Food and Drug Administration. Drugs@FDA and National Drug Code directory, queried via openFDA for testosterone decanoate. openFDA Drugs@FDA; openFDA NDC.
- Drug Enforcement Administration. Schedules of controlled substances: Schedule III, paragraph (f), anabolic steroids. 21 CFR 1308.13. eCFR.
- World Anti-Doping Agency. The 2026 Prohibited List. In effect January 1, 2026. WADA 2026 Prohibited List.