Testosterone suspension is plain testosterone, with no ester attached, ground into fine crystals and suspended in water for intramuscular injection. Because testosterone barely dissolves in water, the crystals sit in the muscle as a depot and dissolve over time. It is one of the oldest injectable forms of the hormone: reports on treating patients with aqueous testosterone suspensions appeared in the medical literature in the 1940s.
Today it is essentially a historical and non-medical product. The US injectable products whose only active ingredient is testosterone itself are all listed as discontinued by the FDA, and no current US label exists. We found no modern human pharmacokinetic study of the aqueous form, so much of what is said about it online cannot be checked.
This page summarizes what drug databases, regulators and the limited published studies report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Drug class | Androgen; anabolic-androgenic steroid (AAS), unesterified testosterone |
| Chemistry | Testosterone, C₁₉H₂₈O₂, 288.4 g/mol |
| Testosterone content | 100% of the labeled milligrams (no ester weight) |
| Form and route | Crystalline testosterone in a water-based vehicle, intramuscular injection |
| US products | Three generic testosterone injections (25, 50 and 100 mg/mL) approved in 1983; all listed as discontinued |
| Half-life | Circulating testosterone: 10–100 minutes (label). No human data on how long the injected depot lasts |
| Key mechanism fact | Release depends on crystals dissolving, not on an ester being cleaved |
| US schedule | Schedule III controlled substance (testosterone, including its salts and esters) |
| WADA status | Prohibited at all times (S1.1 anabolic androgenic steroids) |
What it is
Testosterone was isolated from bull testes and first chemically synthesized in 1935. Because it was ineffective by mouth, it was first given as implanted pellets and then as injectable esters (Nieschlag & Nieschlag, Asian J Androl 2014). Water-based crystal suspensions were another early approach. Papers from 1946 to 1952 describe aqueous or crystal suspensions of testosterone, testosterone propionate and testosterone isobutyrate (Sevringhaus & Sikkema, JCEM 1946; Freed, JCEM 1946; Ragab & El-Itribi, J Egypt Med Assoc 1949; Ercoli & Koller, Farmaco 1949; Drescher, Dtsch Med Wochenschr 1952). These older reports have no abstracts in PubMed and are not controlled trials, so we do not quote results from them.
The molecule in the vial is the same testosterone the body makes: C₁₉H₂₈O₂, molecular weight 288.4 g/mol (PubChem). PubChem lists its solubility in water as 23.4 mg/L at 25 °C, or about 0.023 mg/mL. A 100 mg/mL suspension therefore holds over 4,000 times more testosterone than the water can dissolve. Most of the dose stays as solid crystals until it dissolves at the injection site.
This is the key difference from the esters. With oil-based esters, the ester makes testosterone less polar, so it is absorbed slowly from the oil depot (Depo-Testosterone label). In a suspension there is no ester and no oil; the release rate depends on the crystals. Because there is no ester, every milligram is testosterone (PubChem):
| Form | Molecular weight | Testosterone share by weight |
|---|---|---|
| Testosterone suspension (unesterified) | 288.4 g/mol | 100% |
| Testosterone propionate | 344.5 g/mol | ≈84% |
| Testosterone enanthate | 400.6 g/mol | ≈72% |
| Testosterone cypionate | 412.6 g/mol | ≈70% |
The library also has a page for testosterone base, which covers the same unesterified molecule. Unesterified testosterone is also the active ingredient in testosterone gels.
How it behaves in the body
Once dissolved, it is ordinary testosterone. Per the testosterone labels:
- about 98% of testosterone in plasma is bound to sex-hormone-binding globulin (SHBG) and about 2% is free;
- it acts on the androgen receptor and is converted to two active metabolites, dihydrotestosterone (DHT) and estradiol;
- about 90% of a dose is excreted in the urine as glucuronide and sulfate conjugates.
(Depo-Testosterone label; AndroGel 1.62% label)
The AndroGel label notes that reported half-lives of circulating testosterone vary widely, from 10 to 100 minutes. That figure describes testosterone already in the blood. It does not describe how long an injected suspension keeps releasing hormone, which depends on how quickly the crystals dissolve.
What is known about depot duration
We found no published modern study measuring testosterone levels in people after an aqueous testosterone suspension. The only controlled pharmacokinetic data are from horses:
| Study (horses, not humans) | Design | Finding |
|---|---|---|
| Moeller et al., J Vet Pharmacol Ther 2011 | Aqueous testosterone suspension, IM in the neck, 20 Thoroughbreds | Rapid initial absorption, then a much more variable second absorption phase; median terminal half-life 39 h |
| Ho et al., Drug Test Anal 2015 | Testosterone Suspension 100, six geldings | Detectable for 14 days on average (maximum 18 days in plasma, 20 days in urine) |
The horse study recommended a 30-day withdrawal period before racing. These numbers show that a suspension depot can last far longer than the minutes-long half-life of circulating testosterone. They should not be read as human values.
Laboratory work on testosterone and testosterone-prodrug suspensions found that release in vitro slowed with lower water solubility and larger particle size (Li et al., Drug Deliv Transl Res 2024). For an unregulated product, particle size is not stated or controlled, so its release profile is unknown.
Is suspension “fast-acting” or “short-lived”? Online sources often say testosterone suspension acts within minutes and is cleared within hours, quoting the plasma half-life of testosterone. That half-life applies to hormone already in the blood. No human study we could find measured how long a suspension depot releases testosterone, and in horses it was detectable for about two weeks.
Regulatory status
United States
Drugs@FDA lists three injectable generics whose active ingredient is testosterone itself rather than an ester. The database does not state their vehicle, and no labels are posted.
| Application | Sponsor | Strength | Approved | Status |
|---|---|---|---|---|
| ANDA 086420 | Watson Labs | 25 mg/mL | May 10, 1983 | Discontinued |
| ANDA 086419 | Watson Labs | 50 mg/mL | August 23, 1983 | Discontinued |
| ANDA 086417 | Dr. Reddy’s | 100 mg/mL | July 7, 1983 | Discontinued |
The other Drugs@FDA products with testosterone itself as the active ingredient are gels, skin solutions, patches, a buccal tablet, a nasal gel and pellets, not injections (openFDA Drugs@FDA). Testosterone, including its salts, esters and ethers, is a Schedule III controlled substance (21 CFR 1308.13).
Sport
Testosterone is named in class S1.1 (anabolic androgenic steroids) of the WADA list and is prohibited in and out of competition when administered exogenously (WADA 2026 Prohibited List). Aqueous testosterone is also given to horses, and the horse studies above were done to set detection thresholds and withdrawal times in racing.
What the research shows
There are no controlled human trials of testosterone suspension on muscle, strength or any clinical outcome. The 1940s reports listed above are early clinical descriptions, not randomized trials.
The hormone itself is extremely well studied. Trials of testosterone esters, such as the 600 mg/week enanthate trial in trained men, are covered on the testosterone cypionate and testosterone enanthate pages. Once dissolved, suspension delivers the same molecule, but because its absorption in humans has not been measured, those dose-response data cannot be translated into a suspension dose.
Side effects and risks
No label for testosterone suspension is available. The risks below are class effects of testosterone listed in a current testosterone injection label, and they apply to the hormone regardless of vehicle (Depo-Testosterone label).
Hormonal suppression and fertility
Exogenous testosterone suppresses the pituitary hormone LH and therefore the body’s own testosterone production. At large doses it also suppresses FSH and sperm production; the label lists oligospermia (low sperm count) at high dosages.
Blood, heart and blood pressure
The label’s warnings and precautions include:
- polycythemia (too many red blood cells), with periodic hemoglobin and hematocrit checks advised on long-term therapy;
- venous thromboembolism, including deep vein thrombosis and pulmonary embolism;
- increased blood pressure, which can raise cardiovascular risk over time;
- edema, with or without heart failure, in people with heart, kidney or liver disease;
- an inconclusive evidence base on major adverse cardiovascular events, with some but not all studies reporting increased risk.
Other labeled effects
- gynecomastia (breast tissue growth in men), which occasionally persists;
- acne, oily skin, male-pattern hair loss and hirsutism;
- changes in libido, headache, anxiety and depression;
- in children, premature fusion of growth plates that can reduce adult height.
Abuse
The label states that testosterone has been abused, typically at doses above those recommended and together with other AAS. It warns that such abuse can cause serious cardiovascular and psychiatric adverse reactions, and that the drug has not been shown to be safe and effective for enhancing athletic performance.
Who should not use it
Contraindications in the testosterone injection label include:
- breast cancer in men, and known or suspected prostate cancer;
- pregnancy, because testosterone can virilize a female fetus;
- serious heart, liver or kidney disease;
- known hypersensitivity.
The label also notes that androgens may increase sensitivity to oral anticoagulants (blood thinners) and may lower insulin needs in people with diabetes.
Quality and contamination
With no approved US product on the market, testosterone suspension encountered today comes from outside regulated pharmacies. A Brazilian Federal Police analysis of 345 seized AAS products found that about 42% of the medicines were counterfeit, including 12.0% of aqueous suspensions and 65.2% of oil solutions, and that 11% were substandard (Neves & Caldas, Forensic Sci Int 2017). That study covered AAS products in general, not testosterone suspension alone. Particle size, sterility and actual content of unregulated suspensions are unknown.
Key takeaways
- Plain testosterone, no ester. The suspension is crystalline testosterone in water, so every labeled milligram is testosterone, versus about 70–84% for common esters.
- Release depends on the crystals. Testosterone dissolves poorly in water (23.4 mg/L), so the injected crystals form a depot whose release rate depends on dissolution and particle size.
- A blood half-life is not a depot half-life. The 10–100 minute figure is the half-life of testosterone already in blood. No human study has measured how long a suspension depot lasts; in horses it was detectable for about two weeks.
- No current US product. All three unesterified testosterone injections in Drugs@FDA are discontinued, and testosterone remains Schedule III and banned by WADA.
- Thin evidence, known class risks. There are no controlled human trials of the suspension itself, but the hormone’s labeled risks, including suppression of fertility, polycythemia, blood clots and blood pressure increases, still apply.
Sources
- Nieschlag E, Nieschlag S. Testosterone deficiency: a historical perspective. Asian J Androl. 2014;16(2):161–168. PubMed.
- Sevringhaus EL, Sikkema S. Therapy with aqueous suspensions of testosterone. J Clin Endocrinol Metab. 1946;6(6):415–419. PubMed.
- Freed SC. Therapeutic use of testosterone in aqueous suspension. J Clin Endocrinol Metab. 1946;6(8):571–574. PubMed.
- Ragab AF, El-Itribi A. Perandren therapy with tablet implants and crystals in aqueous suspension in ten cases of male hypogonadism and impotence. J Egypt Med Assoc. 1949;32(1):78–89. PubMed.
- Ercoli A, Koller M. Protracted activity of an aqueous suspension of testosterone propionate [in Italian]. Farmaco Sci Tec. 1949;4(1):31–39. PubMed.
- Drescher H. Experiences with a new testosterone isobutyrate crystal suspension [in German]. Dtsch Med Wochenschr. 1952;77(14):431–432. PubMed.
- National Center for Biotechnology Information. Testosterone, PubChem CID 6013. PubChem.
- Pfizer. Depo-Testosterone (testosterone cypionate) injection, prescribing information. DailyMed.
- AndroGel (testosterone) gel 1.62%, prescribing information. DailyMed.
- Moeller BC, Sams RA, Guinjab-Cagmat J, et al. An interlaboratory study of the pharmacokinetics of testosterone following intramuscular administration to Thoroughbred horses. J Vet Pharmacol Ther. 2011;34(6):588–593. PubMed.
- Ho EN, Kwok WH, Leung DK, et al. Control of the misuse of testosterone in castrated horses based on an international threshold in plasma. Drug Test Anal. 2015;7(5):414–419. PubMed.
- Li S, Wang Z, Yu J, et al. Intramuscularly injected long-acting testosterone-cholesterol prodrug suspension with three different particle sizes: extended in vitro release and enhanced in vivo safety. Drug Deliv Transl Res. 2024;14(4):1093–1105. PubMed.
- US Food and Drug Administration. Drugs@FDA: testosterone injectable, ANDA 086420, ANDA 086419 and ANDA 086417; testosterone product listing via openFDA Drugs@FDA.
- US Drug Enforcement Administration. Schedule III, 21 CFR 1308.13. eCFR.
- World Anti-Doping Agency. The 2026 Prohibited List. WADA 2026 Prohibited List.
- Neves DBDJ, Caldas ED. GC-MS quantitative analysis of black market pharmaceutical products containing anabolic androgenic steroids seized by the Brazilian Federal Police. Forensic Sci Int. 2017;275:272–281. PubMed.