Ostarine (MK-2866)
Also known as: MK-2866, Enobosarm, GTx-024, S-22
Overview
Ostarine (MK-2866, Enobosarm) is one of the most extensively studied Selective Androgen Receptor Modulators (SARMs). Developed by GTx Inc. (now Onconova) and Merck, it was investigated in Phase II/III clinical trials for cancer cachexia, muscle wasting in patients with non-small cell lung cancer, and stress urinary incontinence. Ostarine is the benchmark SARM for comparison in the research community due to its substantial clinical dataset and relatively well-characterized safety profile. It selectively activates androgen receptors in muscle and bone tissue while producing fewer androgenic effects in the prostate and skin compared to anabolic steroids.
Mechanism of Action
Ostarine binds to androgen receptors (AR) with high affinity and selectivity. Unlike testosterone, it produces a tissue-selective conformational change in the AR that activates muscle and bone anabolic pathways while having reduced activity in androgenic tissues (prostate, skin, scalp). This tissue selectivity is mediated by differential recruitment of coactivator proteins. Ostarine activates PI3K/Akt/mTOR signaling in skeletal muscle, driving protein synthesis, nitrogen retention, and satellite cell activation. Bone anabolic effects occur through osteoblast AR stimulation.
Potential Benefits
- Significant lean muscle mass preservation and modest gains (1-3 kg in clinical trials)
- Bone mineral density improvement
- Reduced muscle wasting in cancer and chronic disease models
- Improved physical function in older adults with sarcopenia
- Lower androgenic side effect profile vs. anabolic steroids
- Oral bioavailability (~99%)
Dosage Protocols
The following reflects doses used in published research studies. This is not medical advice. Consult a qualified healthcare professional.
| Typical Range | 10-25 mg/day |
| Beginner | 10 mg/day |
| Intermediate | 15-20 mg/day |
| Advanced | 25 mg/day |
| Cycle Duration | 6-8 weeks |
| Cycle Off | 4-8 weeks (post-cycle therapy may be advisable at higher doses) |
Clinical dose for muscle wasting was 1-3 mg; research/performance doses are 10-25 mg. Once-daily oral administration. Post-cycle support recommended after cycles >8 weeks or doses >25 mg.
Use our Reconstitution Calculator to determine exact syringe units for your protocol.
Routes of Administration
Oral (Capsule/Tablet) Varies — typically moderate for oral-stable compounds
Take with or without food as specified. Follow product labeling for timing.
Read our full Routes of Administration Guide for detailed comparison of all delivery methods.
Stacking Protocols
Popular research stacks involving Ostarine (MK-2866):
Anabolic Recovery Stack
Combines Ostarine (MK-2866) with healing (BPC-157) and GH-axis support (CJC-1295 + Ipamorelin) for comprehensive muscle growth and recovery.
Explore our complete Peptide Stacking Guide for more combinations and safety considerations.
Reconstitution
| Typical Vial Size | N/A — oral capsules or liquid suspension (10-25mg/ml) |
|---|---|
| BAC Water | N/A — oral formulation |
| Storage | Store at room temperature 15-25°C; protect from moisture and light |
| Shelf Life | 24-36 months sealed |
Need exact syringe measurements?
Amino Acid Sequence
N/A — non-peptide small molecule SARM (nonsteroidal)
Side Effects & Safety
- Mild testosterone suppression (dose-dependent; generally mild at ≤25 mg/day)
- Possible lipid profile changes (LDL increase, HDL decrease)
- Liver enzyme elevation possible at higher doses
- Visual disturbances reported anecdotally (mechanism unclear)
- Not androgenic at standard doses but suppression requires PCT consideration
Safety & Contraindications
This information is for educational purposes only. Consult a qualified healthcare provider before using any peptide.
Pregnancy / Lactation
Bleeding Disorders
Active Skin Infection at Injection Site
Pharmacokinetics
| Half-Life | ~24 hours |
|---|---|
| Storage | Store liquid/capsules at room temperature in a dark, dry place. Do not refrigerate oil-based solutions. |
Synergistic Compounds
The following compounds have been studied alongside Ostarine (MK-2866) for potential complementary or synergistic effects:
Learn More
References & Further Reading
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