What it is
Ostarine, also known as MK-2866 and by the development name Enobosarm (GTx-024), is a SARM (selective androgen receptor modulator). It is an orally active non-steroidal compound that activates the androgen receptor to build or preserve muscle and bone, with the intent of having less effect on other tissues than traditional anabolic steroids.
Important framing for this forum: Ostarine is not a peptide. It is a small synthetic drug, included here for completeness alongside the peptides. Of the well-known SARMs it is generally considered the mildest and is often the one beginners reach for first, but “mildest” does not mean “side-effect-free”, and it is still suppressive. It reached late-stage (Phase 3) human trials for muscle wasting but is not an approved medicine for athletic or cosmetic use anywhere, and it is banned in sport (WADA lists SARMs as anabolic agents). Ostarine is one of the most common causes of SARM anti-doping violations, often via contaminated supplements.
What people use it for
People use Ostarine to preserve muscle during a calorie deficit (“cutting”), for modest lean-mass gains, for recomposition, and sometimes for joint or recovery reasons. In clinical research it was studied for muscle wasting (cachexia) and age-related muscle loss (sarcopenia), where it did show measurable improvements in lean body mass. There is no approved indication for physique or performance use.
Typical dose range
There are no approved recreational dosing guidelines. Clinical trials used low doses, around 1 to 3 mg/day, and still showed statistically significant lean-mass improvements. Reported recreational use is typically higher, often around 10 to 25 mg/day. As with all of these compounds, higher doses and longer runs increase suppression and risk without proportionate evidence of benefit.
Note on the calculator: Ostarine is taken orally, so there is no reconstitution step the way there is with injectable peptides. The dosing calculator at Peptide Calculator - Reconstitution & Dosage | Buy Peptides UK is built for reconstituting and dosing injectable/lyophilised compounds, so it does not really apply to an oral SARM. It is linked here only for consistency with the rest of the library.
Half-life and frequency
Reported half-life is roughly 14 to 24 hours, which supports once-daily dosing. As with the other SARMs, the compound and its suppressive effect clear over a day or more after stopping rather than instantly.
How it is taken (oral vs injectable, reconstitution if relevant)
Ostarine is taken orally (capsules or oral liquid). There is no reconstitution. It is processed by the liver, so the liver-related caution that applies to SARMs as a class applies here too.
Common side effects (including suppression)
- Testosterone suppression: milder than RAD-140 or LGD-4033 at low doses and short durations, but still real, especially at the higher doses and longer cycles people actually use (see the next section).
- Lipids: like other SARMs, it can lower HDL (“good” cholesterol), more so at higher doses.
- Liver: SARMs as a class have documented drug-induced liver injury case reports; while Ostarine is considered milder, the class-level caution and the need to watch liver enzymes still apply.
- Headache, fatigue, and mild mood changes are reported anecdotally.
- Product contamination: independent testing frequently finds SARM products that are mislabeled, under- or over-dosed, or contain a different compound. Mass-spectrometry surveys have found a large share of “SARM” supplements did not contain what the label claimed.
PCT and recovery (SARMs)
Ostarine is described as minimally suppressive at lower doses (for example around 25 mg/day for 4 weeks or less), which is why it is often the beginner pick. But “minimally suppressive” is not “non-suppressive”: at higher doses or longer durations, suppression of testosterone, LH, and FSH becomes more meaningful, and some users will need recovery support even from a moderate run.
What suppression means in practice: while the drug is active your body slows its own testosterone production, which can cause low libido, fatigue, and low mood, and can take time to normalise after stopping.
Post-cycle therapy (PCT): for short, low-dose runs some users recover without a SERM, relying on bloodwork to confirm. For higher doses, longer cycles, or anyone showing suppression on labs, a SERM-based PCT (enclomiphene, tamoxifen/Nolvadex, or clomiphene/Clomid) is the standard approach to help the natural axis restart. These are prescription drugs with their own side effects, so the decision should be guided by bloodwork rather than habit.
The honest way to know your status, as with any SARM, is bloodwork: total and free testosterone, LH, FSH, oestradiol, liver enzymes (ALT/AST), and a lipid panel, ideally before, during, and after.
Evidence grade
Moderate by SARM standards, weak by medical standards. Ostarine has the most human clinical data of the SARMs in this library, including Phase 3 muscle-wasting trials that showed lean-mass benefit (though it did not clear the bar to become an approved drug). That is more than most SARMs can claim. Even so, the data is in patient populations and for medical endpoints, not in healthy people using it for physique, and long-term safety at recreational doses is not established.
Honest unknowns
- Long-term safety in healthy users is unknown.
- Suppression and recovery at the higher doses people actually use (versus the 1 to 3 mg trial doses) are not well characterised.
- Liver-injury risk specific to Ostarine is not well quantified; the class-level signal exists.
- Cardiovascular impact of sustained HDL reduction is unclear.
- Real-world product purity and dosing are unreliable, which undermines even careful protocols.
Research use only. Not medical advice. 18+.