Prohormones are compounds that are inactive or weakly active on their own and are converted by enzymes in the body into an active androgen. The name is literal: a precursor to a hormone. The category is broad. This guide sets out the pharmacology and points to the compound pages for each product we stock. It also covers the research record, the legal position and how prohormones differ from SARMs.
What is a prohormone?
In short: a prohormone is a precursor that enzymes convert into an active hormone, usually an androgen such as testosterone or nandrolone.
The body makes its own prohormones. DHEA and androstenedione, produced by the adrenal glands and gonads, are natural steps on the route to testosterone and oestradiol. The products sold as prohormones are either these natural intermediates or synthetic compounds designed to convert into, or behave like, a more potent androgen. The pharmacology of the anabolic steroids these compounds relate to is reviewed by Kicman in the British Journal of Pharmacology (2008).
How prohormones work
In short: liver and tissue enzymes convert the prohormone into the target hormone, often inefficiently.
A prohormone is taken orally and passes through the liver, where enzymes such as 3 beta hydroxysteroid dehydrogenase and 17 beta hydroxysteroid dehydrogenase convert it to the target hormone. Androstenedione converts to testosterone. 1-androstenediol converts to 1-testosterone. 19-norandrostenedione converts to nandrolone.
The conversion rate is often low, sometimes under ten percent, which is why early prohormones produced small effects in the studies that tested them. Some of the material is also converted to oestrogens, which explains several of the findings in those studies.
Two generations of prohormones
In short: the first generation were natural hormone precursors; the second were synthetic designer compounds that are active as taken or convert very efficiently.
The first generation, sold widely as supplements in the United States in the late 1990s, included androstenedione, androstenediol, 19-norandrostenedione and DHEA. Many of these were later brought under US controlled substance law by the Anabolic Steroid Control Act of 2004.
The second generation solved the conversion problem by skipping it. Compounds such as epistane (methylepitiostanol), M-Sten (methylstenbolone) and trenavar (trendione) are either active as taken or convert very efficiently to a potent androgen. Many carry a 17 alpha methyl group that protects them from first pass liver metabolism, which is the modification associated with their liver toxicity.
What the research says
In short: the first generation has small controlled trials showing little benefit and unwanted hormone changes; the second generation has almost no controlled research, only case reports and product analyses.
The first generation has controlled trials. Androstenedione was studied in the late 1990s (King and colleagues, JAMA, 1999): eight weeks of supplementation in young men did not increase testosterone or strength beyond training alone but did raise oestrogen and lower HDL. Leder and colleagues (JAMA, 2000) found that larger amounts of androstenedione raised testosterone in some men, along with oestradiol. Brown and colleagues (Journal of Applied Physiology, 1999) reported that oral DHEA did not raise serum testosterone or improve training adaptations in young men.
The second generation has almost no controlled research. What exists is case reports, most of them describing liver injury with cholestatic jaundice after methylated compounds, and a small number of analytical studies confirming what the products contain. Nasr and Ahmad (Digestive Diseases and Sciences, 2009) described severe cholestasis with kidney failure linked to a methylated designer compound, and Shah and colleagues (Clinical Gastroenterology and Hepatology, 2008) described five cases of cholestatic liver injury. Our guide SARMs versus prohormones sets the classes side by side with sources.
Contamination and labelling
In short: analyses of supplements have repeatedly found undeclared steroids, so what is on the label cannot be assumed.
Catlin and colleagues (JAMA, 2000) found that over-the-counter androstenedione products could contain traces of other steroids, enough to produce positive anti-doping results for a nandrolone metabolite. An international study by Geyer and colleagues (International Journal of Sports Medicine, 2004) found anabolic steroids in a proportion of non-hormonal supplements, and Abbate and colleagues (Drug Testing and Analysis, 2015) reported anabolic steroids in bodybuilding dietary supplements. These findings are the main argument for batch testing in this category.
Prohormones and SARMs are not the same thing
In short: SARMs bind the androgen receptor directly and are not steroids; prohormones are steroids or steroid precursors.
SARMs such as Ostarine and Ligandrol are molecules that bind the androgen receptor directly and selectively. They do not convert to other hormones, do not aromatise to oestrogen, and are not 17 alpha methylated. The difference matters for side effects and for liver load.
The UK position
In short: no prohormone is a licensed medicine, some may fall within the legal definition of anabolic steroids, and all are banned in sport.
No prohormone is a licensed medicine. Every prohormone is an unlicensed medicine if sold for human use under the Human Medicines Regulations 2012, which is why they are sold for research only. Anabolic steroids are listed in Class C of the Misuse of Drugs Act 1971 by name and by a structural definition, so whether a particular compound is captured depends on its chemistry, and the position should be checked compound by compound. In sport, anabolic androgenic steroids and their precursors are prohibited at all times under section S1.1 of the WADA list. The position for SARMs is summarised in Are SARMs legal?
Frequently asked questions
Are prohormones steroids? Most are steroids or steroid precursors. That is the main chemical difference from SARMs.
Do prohormones raise testosterone? The controlled trials of first generation prohormones found small or inconsistent changes, often with a rise in oestrogen. The second generation has not been studied in controlled trials.
Why are methylated prohormones linked to liver injury? The 17 alpha methyl group slows breakdown in the liver, and case reports describe cholestatic liver injury after these compounds.
Are prohormones legal in the UK? None is a licensed medicine, some may be controlled as anabolic steroids depending on structure, and all are prohibited in sport.
The compounds in the research range
Each compound we stock has its own research overview: Epistane, M-Sten, Trenavar, Armistane and TLB-150. The products are Epistane 10mg, M-Sten 5mg, Trenavar 20mg, Armistane 50mg and TLB-150 5mg, all in the prohormones collection and all independently batch tested with certificates on the lab results page. Given the liver findings in the case literature, batch verification matters more here than anywhere else in the catalogue.
Sources
- Kicman AT (2008). Pharmacology of anabolic steroids. Br J Pharmacol. PubMed 18500378
- King DS et al. (1999). Effect of oral androstenedione on serum testosterone and adaptations to resistance training in young men: a randomized controlled trial. JAMA. PubMed 10359391
- Brown GA et al. (1999). Effect of oral DHEA on serum testosterone and adaptations to resistance training in young men. J Appl Physiol. PubMed 10601178
- Leder BZ et al. (2000). Oral androstenedione administration and serum testosterone concentrations in young men. JAMA. PubMed 10683057
- Catlin DH et al. (2000). Trace contamination of over-the-counter androstenedione and positive urine test results for a nandrolone metabolite. JAMA. PubMed 11086369
- Geyer H et al. (2004). Analysis of non-hormonal nutritional supplements for anabolic-androgenic steroids: results of an international study. Int J Sports Med. PubMed 14986195
- Shah NL et al. (2008). Methasteron-associated cholestatic liver injury: clinicopathologic findings in 5 cases. Clin Gastroenterol Hepatol. PubMed 18187367
- Nasr J, Ahmad J (2009). Severe cholestasis and renal failure associated with the use of the designer steroid Superdrol (methasteron). Dig Dis Sci. PubMed 18720005
- Abbate V et al. (2015). Anabolic steroids detected in bodybuilding dietary supplements: a significant risk to public health. Drug Test Anal. PubMed 25284752
- Misuse of Drugs Act 1971.
- Human Medicines Regulations 2012.
- WADA Prohibited List 2026.
All products on this site are sold for laboratory research use only and are not for human consumption. Nothing in this article is medical or legal advice.