All compounds

Ostarine

Also sold as MK-2866, enobosarm, GTx-024, S-22. Selective androgen receptor modulator (SARM).

Works as advertised, real trade-offs (2 of 5)

Ostarine is the most thoroughly studied SARM and it did produce real lean-mass gains in proper clinical trials — and it suppressed testosterone in those same trials, which is the main thing people take SARMs to avoid.

What it is

Ostarine — enobosarm to the people who developed it — is a selective androgen receptor modulator, made by GTx Inc. It was a serious drug programme with a serious purpose: preventing the muscle wasting that kills people with advanced cancer.

The idea behind SARMs is genuinely elegant. Anabolic steroids build muscle by activating the androgen receptor, but they activate it everywhere, which is where the prostate effects, the hair loss, the acne and the cardiovascular problems come from. A SARM is designed to activate that receptor strongly in muscle and bone while doing much less in other tissues. Muscle without the rest of it.

Ostarine got further than any other SARM. It completed phase 2 trials and went into phase 3. It was never approved, anywhere, for anything — and understanding why is more informative than any warning.

Of everything on this site, ostarine has the best claim to being a real, tested compound rather than a research chemical. That is precisely why it belongs in the band it is in: it works, and it costs something specific.

What it actually does

Ostarine binds the androgen receptor and activates it, preferentially in muscle and bone. In practice: measurable lean mass gain, some strength increase, and considerably less of the acne, hair loss and prostate effect associated with anabolic steroids.

It is weaker than testosterone. People coming from steroids generally find it disappointing; people who have never used anything find it does something noticeable.

The reason people choose ostarine specifically is almost always the same: they want the muscle without shutting down their own testosterone, and without needing injections or post-cycle drugs. That is the promise, and it is worth being precise about how much of that promise is kept.

What the evidence actually shows

On whether it builds muscle: yes, and this is properly established. The phase 2 trial in cancer patients was double-blind, randomised and placebo-controlled, and it found a real increase in lean body mass. That is a higher standard of evidence than almost anything else on this site.

On why it was not approved: the phase 3 programme is the interesting part. Ostarine increased lean body mass — but the trials also had to show that the extra muscle translated into people being able to do more. Physical function did not improve to the standard required. The programme did not lead to approval.

That distinction is worth carrying around. Ostarine reliably changes what a scan of your body composition says. Whether it changes what you can do is a genuinely open question that a well-funded trial programme tried and failed to answer in the affirmative.

On testosterone suppression: it suppresses. This is the finding that matters most for the people actually taking it, and it is not ambiguous. The trials measured it. SARMs act on the same axis your own testosterone production is regulated by, and the body responds by making less. Reviews of the randomised trials consistently report suppression of endogenous testosterone.

So the central promise — muscle without suppression — is not kept. It is suppressed less than by a steroid cycle, and it appears to recover in most people after stopping. But the belief that ostarine is non-suppressive is simply false, and it is the most common false belief about this compound.

On liver injury: there are published case reports of drug-induced liver injury in otherwise healthy young men taking ostarine and other SARMs, some of them severe, presenting as jaundice and markedly abnormal liver enzymes. These are case reports, not trial data, and they represent a small number of people out of a large number of users — so the risk per person is probably low. It is also real, unpredictable, and not something you can feel coming.

What nobody knows: what long-term use does. The trials ran for months, in people who were seriously ill, under medical supervision. Nobody has followed a healthy young man taking SARMs on and off for five years, and nobody can tell you whether suppression always recovers fully.

The risk profile

Works as advertised, real trade-offs (2 of 5) — It does the thing people take it for, and it costs something specific and known.

What going wrong looks like from the inside

Two things go wrong with ostarine, and neither announces itself.

The suppression is invisible while it is happening. You will not feel your testosterone fall while you are taking it — ostarine is occupying the receptor, so the signal your body would normally use to tell you something is wrong is being covered up. The trouble starts after you stop. That is when the fatigue, the flat mood, the loss of motivation and libido, and the sense that recovery from training has stopped working turn up. Many people misread that entirely, concluding that they have simply lost their gains and need to start another cycle — which suppresses them further and delays recovery.

If you are going to take it, the single most useful thing you can do is get bloods done before you start. Without a baseline you cannot tell the difference between “my levels are recovering normally” and “my levels are low and staying there,” and that difference determines whether you need medical help. Almost nobody does this, and it is the cheapest risk reduction available.

The liver injury is the other one, and it is genuinely sudden. In the published cases, healthy young men were fine and then were not. What they noticed first, typically: fatigue out of proportion to anything, then itching without a rash, then dark urine, then yellowing of the eyes. If you get that sequence, particularly the itching and the dark urine, stop taking it and get a liver panel — not next month, that week. It generally resolves after stopping, and it does not always resolve if you keep going.

Interactions and combinations

Ostarine is not a central nervous system depressant and does not carry the fatal-combination risk that dominates the phenibut and tianeptine pages.

The interaction that matters here is with other things that stress the liver, because that is the organ at risk. Alcohol is the obvious one. So is paracetamol/acetaminophen taken regularly, and so are the other oral compounds ostarine is commonly stacked with — including other SARMs and oral anabolic steroids, most of which are more hepatotoxic than ostarine is. Stacking is the norm in this space, and it means that when liver injury does happen, working out what caused it is often impossible.

Cardarine is very commonly sold and stacked alongside ostarine. It is not a SARM, it does not work the same way, and its risk profile is entirely different and considerably worse on the dimension that matters. Do not let their being sold together suggest they are the same class of decision.

Ostarine is banned in all tested sport and is detectable long after the last use. It is also a documented cause of positive tests in athletes who took a contaminated supplement they believed was something else.

If you’re already using it

There is no withdrawal and no need to come off gradually. If you want to stop, stop.

What is worth doing:

Get bloods. A full testosterone panel and a liver panel, both while on it if you can and again a few weeks after stopping. This is the only way to know what actually happened to you rather than guessing from how you feel. Any GP will order these; you do not need to explain your reasoning in detail, though telling them is better.

Know the liver warning signs — fatigue, itching without a rash, dark urine, pale stools, yellowing of the eyes — and act on them the week they appear.

If you feel flat, unmotivated and low-libido weeks after stopping, that is worth investigating rather than treating with another cycle. Suppression that has not recovered is a treatable medical problem, and the trap is that the thing that makes you feel better in the short term is the thing that caused it.

Do not buy post-cycle-therapy drugs from the same vendors. Those are prescription medicines with their own risks, and the supply chain that got roughly half its SARM labelling wrong is not a good place to source them.

This page has not yet been reviewed by a clinician. It was written from the published literature and every claim is cited, but no named medical professional has checked it. We say so here rather than let a missing byline read as an implicit one.

Last reviewed 7 September 2026. Found something wrong? Corrections are published, not silently edited.