SARMs (selective androgen receptor modulators) are synthetic compounds designed to mimic some effects of testosterone, particularly building muscle and strengthening bone, while theoretically avoiding the broader hormonal side effects of traditional anabolic steroids. They were originally developed as potential treatments for muscle-wasting conditions like cancer cachexia and age-related sarcopenia, but none have received FDA approval. Most people encounter SARMs through the fitness and bodybuilding world, where they’re sold in a legal gray area and marketed as a “safer” alternative to steroids.
How SARMs Work in the Body
SARMs bind to the same androgen receptors that testosterone does, but with a twist. Traditional steroids activate androgen receptors across the entire body, including in the prostate, skin, and scalp, which is why they cause side effects like acne, hair loss, and prostate enlargement. SARMs are designed to be selective: they trigger muscle and bone growth while producing less activity in other tissues.
This selectivity comes from the shape SARMs take when they dock into the androgen receptor. Different ligands cause the receptor to fold into slightly different three-dimensional shapes, and those shapes attract different helper proteins (called coregulators) depending on the tissue. In muscle and bone cells, SARMs recruit coregulators that promote growth. In prostate cells, they activate different signaling pathways than testosterone does, which is partly why their androgenic effects are reduced. Research on one SARM showed that it triggered a completely different chain of cellular signals in prostate cells compared to the natural hormone, while both produced similar growth-promoting signals in bone cells.
Another reason SARMs appear more selective in animal studies is simpler than it sounds: unlike testosterone, SARMs aren’t broken down by the same enzymes that convert testosterone into its more potent form in tissues like the prostate and skin. Some researchers argue that this metabolic difference, rather than true receptor selectivity, accounts for a significant portion of the favorable ratios seen in preclinical testing.
Effects on Muscle and Body Composition
The primary draw of SARMs is their ability to increase lean body mass. In a clinical trial of cancer patients experiencing muscle wasting, those taking enobosarm (also known as Ostarine or MK-2866) gained a median of 1.5 kg of lean mass over roughly 16 weeks, while the placebo group gained essentially nothing. That’s a meaningful difference for people losing muscle to disease, though it’s modest compared to what anabolic steroids produce in healthy bodybuilders.
A systematic review of nine randomized controlled trials covering 970 patients found that SARMs generally had a positive effect on both physical performance and body composition. The average follow-up was about 80 days, and most adverse effects were mild to moderate. These trials used clinical doses far lower than what recreational users typically take, which matters when weighing the risk-benefit picture.
In animal research, RAD-140 (Testolone) preserved both lean mass and bone mineral density in aging male mice. The bone density preservation was statistically significant, and treated mice also showed lower levels of a key inflammatory marker. Notably, these benefits appeared only in male mice, not females, highlighting how much the effects can vary.
Hormonal Suppression
One of the most important things SARMs do is suppress your body’s own testosterone production. This is often downplayed in marketing but is well-documented in clinical research. In a study of healthy young men taking LGD-4033 (Ligandrol), total testosterone levels dropped in a dose-dependent manner over 21 days. At the highest dose tested (1.0 mg per day, still far below what many recreational users take), free testosterone was also suppressed, and follicle-stimulating hormone levels dropped as well.
The good news from that study: hormone levels returned to baseline by day 56 after stopping the drug. But that recovery timeline was observed at clinical doses taken for just three weeks. Recreational users often take higher doses for 8 to 12 weeks, and recovery may take significantly longer. During that suppressed period, you can experience fatigue, low libido, mood changes, and loss of the muscle you gained.
This suppression is why many SARM users pursue “post-cycle therapy” (PCT), borrowing a practice from the steroid community. PCT typically involves drugs that stimulate the body’s hormonal axis to restart natural testosterone production. However, no randomized controlled trials support PCT for this purpose, and no clinical guidelines exist for managing hormone suppression caused by SARMs or steroids. Users who reported using PCT said it reduced their withdrawal symptoms and cravings to restart by roughly 60%, though researchers note some of that benefit could be placebo.
Cardiovascular Risks
SARMs consistently lower HDL cholesterol, the type that protects against heart disease. A 12-week dose-ranging study found clear, dose-dependent drops in HDL levels. At 1 mg per day, HDL fell by about 5 mg/dL. At 5 mg per day, it dropped by 13 mg/dL. At 15 mg per day, HDL plummeted by over 18 mg/dL. For context, every 1 mg/dL decrease in HDL is associated with a 2 to 3 percent increase in cardiovascular risk.
The mechanism behind this drop involves increased activity of an enzyme that breaks down HDL particles. This is the same pattern seen with traditional anabolic steroids, which means SARMs don’t offer the cardiovascular safety advantage many users assume. The FDA lists increased risk of heart attack and stroke among the potential dangers of SARM-containing products.
Liver Damage
Published case reports document serious liver injury in young, otherwise healthy men using SARMs. In two cases, a 19-year-old and a 28-year-old developed severe cholestatic liver injury, where bile flow becomes blocked within the liver. The 28-year-old’s bilirubin levels reached more than 23 times the upper limit of normal. Liver biopsies in both cases showed bile duct destruction, bile plugs clogging the tissue, and cell death. Neither had prior liver disease.
These aren’t isolated incidents. The FDA has documented life-threatening liver reactions, including cases requiring hospitalization and acute liver failure, in people taking products labeled as SARMs. Because most SARMs are sold as “research chemicals” without pharmaceutical quality control, the actual contents of what you’re taking may differ from the label, which compounds the risk.
Regulatory Status and Product Quality
SARMs are not approved by the FDA for any medical use. They are not legal dietary supplements, despite frequently being marketed as such. The FDA has issued warning letters to companies selling them and pursued criminal charges against distributors. The World Anti-Doping Agency (WADA) has banned SARMs in competitive sports, and advanced testing can detect certain SARM metabolites for weeks after use. One metabolite of LGD-4033 was still detectable in urine more than 40 days after the last dose, even at very small amounts.
Independent lab testing of products sold as SARMs has repeatedly found problems: wrong compounds, wrong doses, unlisted ingredients, or contamination with actual anabolic steroids. A study that analyzed dozens of SARM products purchased online found that only about half contained the compound listed on the label, and nearly 40% contained unlisted substances. This means you may not even be taking what you think you’re taking.
The Full List of Reported Side Effects
Beyond hormonal suppression, cardiovascular changes, and liver damage, the FDA’s warning includes these additional risks associated with SARM use:
- Sexual dysfunction, including reduced libido and erectile problems during and after use
- Testicular shrinkage, from suppressed gonadotropin signaling
- Infertility, due to reduced sperm production
- Sleep disturbances
- Psychosis and hallucinations, reported in some cases
- Pregnancy miscarriage, if taken by or transferred to a pregnant person
Many of these overlap with the side effects of anabolic steroids, which undercuts the central marketing claim that SARMs are fundamentally safer. The tissue selectivity that looks promising in lab settings and animal models has not translated into a clean safety profile in real-world human use, particularly at the doses recreational users favor. The gap between what SARMs are designed to do in theory and what they actually do in practice remains significant.