Prohormones vs SARMs: What Is the Difference?

Both categories grew up in the supplement industry, often in the same stores and under similar marketing. They are chemically very different, though. Here is how to tell them apart and what each means for your health.

What prohormones are

Strictly, a prohormone is a precursor that the body converts into an active hormone. Androstenedione (“andro”), made famous in 1998 when baseball player Mark McGwire said he used it, is converted to testosterone. DHEA is converted, in small amounts, to testosterone and estrogen.

In the 2000s, the term was stretched to cover “designer” compounds such as methasterone (Superdrol) and methyl-1-testosterone. Many were not precursors at all but active oral steroids, sold over the counter through legal loopholes. Liver injury reports followed. The United States banned most of them under the Anabolic Steroid Control Act of 2004 and later updates. In Canada, anabolic steroids and their derivatives fall under Schedule IV of the Controlled Drugs and Substances Act. See our Superdrol guide.

What SARMs are

Selective androgen receptor modulators were developed by drug companies from the late 1990s to treat muscle wasting and osteoporosis with fewer side effects than steroids. They are not steroids and are not converted into hormones. They bind the androgen receptor directly, with more effect in muscle and bone. None has been approved. See SARMs 101.

Side by side

The real risks

Prohormones

• Liver injury, sometimes severe, especially with methylated designer compounds
• Gynecomastia and water retention with those that convert to estrogen
• Sharp HDL drops and higher blood pressure
• Suppression of natural testosterone

SARMs

• Dose-dependent suppression of testosterone, LH and FSH
• HDL drops within weeks
• Case reports of liver injury
• Specific effects, such as vision changes with S4 (andarine)
• Unreliable product quality

Why both left the supplement shelf

The pattern was similar for both. A compound appeared in stores or online with supplement-style marketing, sales grew quickly, and reports of side effects followed. With designer prohormones, the warning signs were liver injury and hormone disruption; the US Food and Drug Administration issued warnings, and laws were changed to control them. With SARMs, the FDA warned in 2017 that products marketed as bodybuilding supplements contained SARMs linked to liver toxicity and heart attack and stroke risk, and has since warned companies selling them. Health Canada has also published advisories about unauthorised products containing SARMs. The lesson is that “sold as a supplement” says nothing about safety: neither category went through the review that approved medicines must pass.

Supplements that are neither

Many “test boosters” sold in Canadian stores contain herbs such as tribulus, fenugreek, ashwagandha or D-aspartic acid. These are not prohormones or SARMs. Evidence for meaningful testosterone increases in healthy men is weak, though some products have been found to contain undeclared drugs. Natural health products sold legally in Canada must carry an eight-digit NPN (Natural Product Number) from Health Canada; products without one have not been reviewed.

Drug testing

Prohormones, designer steroids and SARMs are all prohibited by the World Anti-Doping Agency. Contaminated supplements have caused positive tests for athletes who did not knowingly take anything banned, which is why the Canadian Centre for Ethics in Sport advises tested athletes to use third-party-certified supplements only.

Bloodwork if using either

Liver enzymes, bilirubin, a lipid panel, testosterone, estradiol, LH, FSH and a complete blood count give a clear picture. Arrange tests through your doctor or privately at LifeLabs or Dynacare; see our bloodwork guide.

Frequently asked questions

Photo: rawpixel (public domain).

General information, not medical advice. SARMs are not approved for human use in Canada; anabolic steroids are Schedule IV controlled substances.