Methylstenbolone, sold under names such as M-Sten, Methyl-Sten, Ultradrol and Ultra-Sten, is a synthetic oral anabolic-androgenic steroid (AAS). It is a “designer steroid”: it was never developed as a medicine, and it reached the public through products marketed as bodybuilding “nutritional supplements” in the 2010s.
The single most important fact about it is that no controlled human trial has ever tested it, for muscle, strength or anything else. Everything published in people comes from drug-testing labs that gave single doses to map its urine metabolites, plus case reports of liver injury. In 2017 the FDA told a US seller that a methylstenbolone product was not a legal dietary supplement but an unapproved new drug, and the product was recalled.
This page summarizes what the chemistry databases, the few published studies and regulators report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Drug class | Designer 17α-methylated anabolic-androgenic steroid; DHT derivative (17α-methyl stenbolone) |
| Product names | M-Sten, Methyl-Sten, Ultradrol, Ultra-Sten; also an ingredient in Super DMZ Rx 2.0 |
| Approval | No FDA-approved product and no recognized medical use |
| Route | Oral (capsules marketed as supplements) |
| Formula and weight | C₂₁H₃₂O₂, 316.5 g/mol |
| Human data | Urinary metabolism studies only (single oral doses); no efficacy or safety trials |
| Half-life | No published human half-life; unchanged drug detectable in urine for ≈45 h after a single dose in one study |
| US status | Not named in the Schedule III list; FDA says it is not a dietary ingredient (2017 warning letter) |
| WADA status | Prohibited at all times (S1.1 anabolic androgenic steroids, as a structurally similar substance) |
What it is
Methylstenbolone’s chemical name is 2,17α-dimethyl-17β-hydroxy-5α-androst-1-en-3-one (Cavalcanti et al., Steroids 2013). PubChem lists the formula C₂₁H₃₂O₂ and a molecular weight of 316.5 g/mol (PubChem CID 252380). It is built on the dihydrotestosterone (DHT) skeleton and sits in a small family of closely related steroids:
| Steroid | Chemical name | How it relates to methylstenbolone |
|---|---|---|
| Stenbolone | 17β-hydroxy-2-methyl-5α-androst-1-en-3-one | Same molecule without the 17α-methyl group |
| Methasterone (Superdrol) | 2α,17α-dimethyl-17β-hydroxy-5α-androstan-3-one | Same molecule without the double bond between carbons 1 and 2 |
| Methyl-1-testosterone | 17β-hydroxy-17α-methyl-5α-androst-1-en-3-one | Same molecule without the 2-methyl group |
| Methylstenbolone | 2,17α-dimethyl-17β-hydroxy-5α-androst-1-en-3-one | Not named in the US Schedule III list |
Chemical names for the first three are from 21 CFR 1308.13, where all three are listed as Schedule III anabolic steroids. In other words, methylstenbolone is stenbolone with a 17α-methyl group added. This group slows breakdown in the liver and is linked to the liver toxicity of 17α-alkylated steroids (Skrzypiec-Spring et al., J Clin Med 2024). See Stenbolone Acetate, Superdrol (Methasterone) and Methyl-1-Testosterone for those compounds.
The scientific record of methylstenbolone starts with doping-control chemistry. In 2013 a Brazilian lab described it as a new anabolic steroid found in a “nutritional supplement” bought online (Cavalcanti et al., Steroids 2013). A 2014 case report noted it was not a controlled substance in the US at that time and that it had been compared to methasterone (Superdrol), which the FDA had recently acted against (Agbenyefia et al., 2014).
We found no published study measuring how strongly methylstenbolone binds or activates the androgen receptor, and no animal study of its anabolic or androgenic potency. Claims about its strength relative to other steroids, or about “dry” muscle gains, come from product marketing rather than from data.
How it works in the body
There are no human pharmacokinetic studies of methylstenbolone: no measured blood levels, peak times or elimination half-life. What exists are excretion studies run by anti-doping labs to find urine markers.
| Study | Design | Main findings |
|---|---|---|
| Cavalcanti et al., Steroids 2013 | 4 volunteers, single oral dose | Two 16-hydroxylated metabolites detectable for over a week; unchanged methylstenbolone detectable for only ≈45 h |
| Geldof et al., Biomed Chromatogr 2014 | Human liver microsomes and a chimeric mouse model | 10 mono-hydroxylated metabolites in microsomes; the product labeled as methylstenbolone also contained methasterone |
| Piper et al., Drug Test Anal 2019 | Single 10 mg oral dose of isotope-labeled methylstenbolone; urine collected for 29 days | Up to 40 metabolites, mostly glucuronide conjugates; methylstenbolone glucuronide and three other metabolites still detectable on day 29 |
In horses given 100 mg daily for three days, peak plasma levels were only about 0.4–0.7 ng/mL one hour after the last dose, and metabolites were detectable in urine for up to 5 days (Choi et al., J Chromatogr A 2018). This is equine data and does not tell us the kinetics in people.
The 2019 human study found that the two metabolites proposed in 2013 did not show up in real doping samples that had tested positive for methylstenbolone. Labs now rely on newer long-term markers instead (Piper et al., 2019). Routine clinical drug screens may not include it at all: in a Swedish study that reanalyzed 310 urine samples from 2022–2023 with anti-doping methods, 3 contained methylstenbolone, a substance the lab’s routine AAS test did not cover (Bohlin et al., Drug Test Anal 2025).
About half-life figures. Some websites and apps quote a specific half-life for methylstenbolone. We could not find any human study that measured it. The urine detection windows above describe how long traces can be found, not how fast blood levels fall.
Regulatory status
FDA
In June 2017 the FDA sent a warning letter to Hardcore Formulations over its product Ultra-Sten, labeled as containing methylstenbolone (FDA warning letter, 2017). The FDA stated that:
- methylstenbolone is a synthetic steroid, not a “dietary ingredient,” so the product was not a dietary supplement;
- claims such as “Rapid Size and Strength” made it a drug, and an unapproved new drug;
- it was a prescription-type drug because of its potential for harm, so no safe directions for self-use could be written.
The company then recalled all lots of Ultra-Sten, which had been sold nationwide from August 2014 to May 2017 (FDA recall notice, 2017).
DEA and the Controlled Substances Act
Methylstenbolone is not named in the list of Schedule III anabolic steroids in 21 CFR 1308.13. However, the Designer Anabolic Steroid Control Act of 2014 widened the legal definition of “anabolic steroid.” An unlisted substance that is derived from, or substantially similar in structure to, a listed steroid counts as an anabolic steroid, and so falls in Schedule III, if it was made to promote muscle growth or is marketed that way (DEA final rule, Federal Register 2023). Its close relatives stenbolone and methasterone are both listed. Whether a specific product meets that definition is a legal determination, so we do not describe methylstenbolone itself as scheduled.
Sport
The WADA 2026 Prohibited List bans anabolic androgenic steroids at all times (class S1.1). Methylstenbolone is not named, but stenbolone, methasterone and methyl-1-testosterone are, and the class explicitly includes “other substances with a similar chemical structure.” Anti-doping labs report adverse findings for methylstenbolone in athlete samples (Piper et al., 2019).
What the research shows
Muscle, strength and body composition
No randomized or controlled study in humans or animals has measured methylstenbolone’s effect on muscle mass, strength or body fat. No dose has been tested for efficacy or safety. The 10 mg single dose in the 2019 metabolism study was chosen to trace metabolites, not to test any effect (Piper et al., 2019).
Laboratory studies
The remaining research is chemistry. In one cell culture study, methylstenbolone was toxic both to a breast cancer cell line and to normal human skin fibroblasts. Fungal metabolites of the compound were not toxic to the normal cells (Aamer et al., Bioorg Chem 2022). These are in-vitro results and say nothing about effects in people.
Side effects and risks
Because there are no trials, nothing is known about how often side effects occur. The evidence is case reports, regulator warnings and what is known about the 17α-methylated steroid class.
Liver injury
The first published case was a previously healthy 26-year-old man who took Super DMZ Rx 2.0 (10 mg methylstenbolone plus 10 mg dymethazine per capsule) twice daily for 30 days, as the label directed (Agbenyefia et al., 2014). He developed dark urine, pale stools, jaundice and itching. A biopsy showed cholestasis (blocked bile flow inside the liver).
| Measure (normal range) | Day 35 after starting | Day 59 (peak bilirubin) |
|---|---|---|
| Total bilirubin (0.3–1.9 mg/dL) | 19.3 mg/dL | 45.9 mg/dL |
| ALT (10–40 IU/L) | 269 IU/L | 77 IU/L |
| ALP (44–147 units/L) | 132 units/L | 207 units/L |
Bilirubin had fallen to 2.1 mg/dL about 10 weeks after he stopped. This pattern, very high bilirubin with only modest enzyme rises, is typical of steroid-induced cholestasis. Because the product also contained dymethazine, the injury cannot be pinned on methylstenbolone alone.
A review of 50 years of published AAS case reports found methylstenbolone in only five of them. Liver complications were reported in all of its cases, and its link with liver problems was among the strongest found (adjusted p = 0.015) (Skrzypiec-Spring et al., J Clin Med 2024). With so few cases, this shows a reporting pattern, not a measured risk.
More broadly, the US Drug-Induced Liver Injury Network described 44 men with liver injury from bodybuilding supplements. All had jaundice, 71% were hospitalized, and onset came a median of 73 days after starting. Product testing often found anabolic steroids that were not on the label (Stolz et al., Aliment Pharmacol Ther 2019). That study was not specific to methylstenbolone.
Hormonal, cardiovascular and other effects
No study has measured methylstenbolone’s effect on natural testosterone, sperm production, cholesterol or blood pressure. In its recall notice and warning letter, the FDA listed the risks expected from anabolic steroid products of this kind (FDA recall notice, 2017; FDA warning letter, 2017):
- serious liver injury and kidney injury;
- lower HDL (“good”) cholesterol and higher blood pressure, with a possible increase in heart attack and stroke risk;
- testicular shrinkage, male infertility and breast enlargement in men;
- virilization in women, such as a deeper voice, more body hair and menstrual changes;
- short stature in children, and aggressive behavior.
The FDA noted that people with heart, liver or prostate conditions may be at higher risk.
Mislabeled and contaminated products
Methylstenbolone has repeatedly turned up in products that did not contain what their labels said:
- A product sold as methylstenbolone also contained methasterone, and taking it produced mainly methasterone metabolites in urine (Geldof et al., 2014).
- In New York in 2012–2013, about 16 people reported fatigue, hair loss and muscle aches after taking B-50 vitamin and multimineral supplements from one supplier. State lab testing found methasterone, dymethazine and methylstenbolone in the capsules. One person was hospitalized with liver damage, and a child developed severe virilization (Tran et al., Steroids 2023).
- Reviews of designer steroids sold over the counter report hepatotoxicity, cholestasis, kidney failure, hypogonadism (low testosterone), gynecomastia and infertility linked to this product category (Rahnema et al., Andrology 2015).
Key takeaways
- A designer steroid, not a medicine. Methylstenbolone is 17α-methylated stenbolone, sold in “supplements.” It has never been approved or tested as a drug.
- No human efficacy or safety data. The only human studies are single-dose urine metabolism studies. There are no trials, no tested doses and no measured half-life.
- Liver injury is the documented harm. Published cases describe severe cholestatic jaundice, including after 30 days at label doses in a combination product.
- Labels are unreliable. Products sold as methylstenbolone have contained methasterone, and methylstenbolone has been found in vitamin products.
- Regulators treat it as a steroid. The FDA says it is not a lawful dietary ingredient. US law can treat close analogs of listed steroids as Schedule III, and WADA bans it at all times.
Sources
- Cavalcanti GdeA, Leal FD, Garrido BC, et al. Detection of designer steroid methylstenbolone in “nutritional supplement” using gas chromatography and tandem mass spectrometry: elucidation of its urinary metabolites. Steroids. 2013;78(2):228–233. PubMed.
- Geldof L, Lootens L, Polet M, et al. Metabolism of methylstenbolone studied with human liver microsomes and the uPA⁺/⁺-SCID chimeric mouse model. Biomed Chromatogr. 2014;28(7):974–985. PubMed.
- Piper T, Fusshöller G, Schänzer W, et al. Studies on the in vivo metabolism of methylstenbolone and detection of novel long term metabolites for doping control analysis. Drug Test Anal. 2019;11(11-12):1644–1655. PubMed.
- Choi TLS, Wong JKY, Kwok WH, et al. Metabolic study of methylstenbolone in horses using liquid chromatography-high resolution mass spectrometry and gas chromatography-mass spectrometry. J Chromatogr A. 2018;1546:106–118. PubMed.
- Bohlin KP, Villén T, Hopcraft O, et al. Prevalence of AAS-positive samples at Drug Abuse Laboratory Sweden between 2014 and 2023 and sub-study of dual use of AAS and narcotics. Drug Test Anal. 2025;17(12):2421–2428. PubMed.
- National Center for Biotechnology Information. Methylstenbolone, PubChem CID 252380. PubChem.
- Code of Federal Regulations. 21 CFR 1308.13, Schedule III. eCFR.
- Drug Enforcement Administration. Implementation of the Designer Anabolic Steroid Control Act of 2014. Federal Register. August 1, 2023;88:50036 (FR Doc 2023-15747). Federal Register.
- US Food and Drug Administration. Warning letter to Hardcore Formulations, MARCS-CMS 522783. June 5, 2017. FDA.
- Hardcore Formulations. Hardcore Formulations issues voluntary nationwide recall of Ultra-Sten and D-Zine capsules due to labeling that it contains anabolic steroids. Company announcement, June 28, 2017; posted by FDA February 7, 2018. FDA.
- World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2026. WADA 2026 Prohibited List.
- Agbenyefia P, Arnold CA, Kirkpatrick R 3rd. Cholestatic jaundice with the use of methylstenbolone and dymethazine, designer steroids found in Super DMZ Rx 2.0 “nutritional supplement”: a case report. J Investig Med High Impact Case Rep. 2014;2(2):2324709614532800. PubMed; PMC.
- Skrzypiec-Spring M, Rozmus J, Abu Faraj G, et al. Abuse of anabolic-androgenic steroids as a social phenomenon and medical problem-its potential negative impact on reproductive health based on 50 years of case report analysis. J Clin Med. 2024;13(19):5892. PubMed.
- Stolz A, Navarro V, Hayashi PH, et al. Severe and protracted cholestasis in 44 young men taking bodybuilding supplements: assessment of genetic, clinical and chemical risk factors. Aliment Pharmacol Ther. 2019;49(9):1195–1204. PubMed.
- Tran BN, Okoniewski R, Spink BC, et al. Androgenic steroids in over-the-counter dietary supplements: analysis for association with adverse health effects. Steroids. 2023;193:109199. PubMed.
- Rahnema CD, Crosnoe LE, Kim ED. Designer steroids - over-the-counter supplements and their androgenic component: review of an increasing problem. Andrology. 2015;3(2):150–155. PubMed.
- Aamer M, Siddiqui M, Jabeen A, et al. New anti-inflammatory and non-cytotoxic metabolites of methylstenbolone obtained by microbial transformation. Bioorg Chem. 2022;129:106187. PubMed.