Ostarine, also called MK-2866 or enobosarm, has been investigated in animal models of osteoporosis. Those experiments explore bone density, structure and healing. They do not establish that an Ostarine product treats osteoporosis or prevents fractures in people.
What did the bone-density study find?
A study published online in 2018 examined Ostarine in female rats with experimentally induced bone loss. Some bone-density and structural measures improved, with different effects in the thigh bone and spine. However, the researchers found no significant improvement in the mechanical properties they tested. Uterine weight also increased. Read the original study.
This distinction matters: a change in a laboratory measure is not evidence that people will suffer fewer fractures. The authors called for further work on longer-term effects and adverse effects.
Why bone researchers study androgen receptors
In short: androgens help maintain bone, so a compound that acts on the androgen receptor mainly in muscle and bone was an obvious candidate for bone research.
Bone cells carry androgen receptors, and the loss of sex hormones with age or after surgical removal of the ovaries or testes is followed by bone loss in both animals and people. Testosterone itself is not a practical long term option for many patients because of its effects on the prostate, skin and cardiovascular system. SARMs were designed to keep the wanted effect on muscle and bone while reducing the others, which is why several of them were tested in bone models. Narayanan and colleagues (Molecular and Cellular Endocrinology, 2018) review that development history.
The earliest bone data in the class came from other compounds. Andarine (S-4) prevented bone loss in castrated male rats (Gao and colleagues, Endocrinology, 2005) and in ovariectomised female rats (Kearbey and colleagues, Pharmaceutical Research, 2007). Ostarine research builds on that work.
How the rat models work
In short: researchers remove the ovaries or testes of rats to cause hormone related bone loss, then compare treated and untreated animals.
The ovariectomised female rat is the standard laboratory model of bone loss after the menopause, and the orchiectomised male rat is the equivalent for androgen deficiency. Studies then measure bone mineral density, the internal structure of the bone (often by micro computed tomography), and biomechanical strength, usually by bending or compressing the bone until it breaks. A treatment can change density or structure without changing strength, so all three measures matter. Organ weights, such as the uterus or prostate, are also recorded as a check on effects outside bone.
What does later research add?
In short: later rat studies looked at bone healing, male animals and combinations, with mixed results and some safety concerns.
| Research | Main finding and limitation |
|---|---|
| Female-rat bone-healing study, online 2019 | Reported changes in early healing after a controlled bone injury. It did not test recovery from injuries in people. Study |
| Male-rat osteoporosis study, 2023 | Effects depended on when treatment began. Preventive treatment affected more bone measures, but mechanical properties did not improve and prostate weight increased. Study |
| Female-rat combination study, 2025 | Examined Ostarine with raloxifene. Some bone outcomes improved, while organ and blood-chemistry findings raised safety concerns. Combination results cannot be attributed to Ostarine alone. Study |
These are different experiments with different endpoints. Their results should not be combined into a claim that Ostarine builds stronger bones or safely speeds recovery in people.
What has been measured in people?
In short: the human Ostarine trials measured muscle, function and safety, not fractures.
The best known human study, the phase II trial in older men and postmenopausal women reported by Dalton and colleagues in 2011, was designed around lean body mass and physical function. Later trials in cancer related muscle wasting (Dobs and colleagues, 2013) had similar endpoints. We are not aware of a published human trial of Ostarine with fracture rate or bone strength as its main outcome, so the bone question remains an animal research question.
Safety signals in the bone studies
In short: the rat studies recorded effects on the uterus and prostate, which is a reminder that selectivity is partial.
The uterine weight increase in female rats and the prostate weight increase in male rats both show that Ostarine acted outside bone in these models. Human trials of SARMs have also recorded falls in HDL cholesterol and in natural testosterone. Neither finding is unusual for the class, but both mean a bone effect cannot be considered on its own.
Does this establish Ostarine as an osteoporosis treatment?
In short: no. These findings come from rats and do not show that Ostarine prevents fractures in people.
The studies summarised here do not establish a safe, effective osteoporosis treatment for people. Findings about muscle mass in other Ostarine research also do not, by themselves, demonstrate fracture prevention.
For information about diagnosis and treatment choices, see the NHS osteoporosis treatment guide and speak with your healthcare team. Research products are not substitutes for prescribed care.
For the compound's wider research background, read our Ostarine MK-2866 guide.
Frequently asked questions
Has Ostarine been tested for osteoporosis in humans? Not as far as the published literature shows. The bone studies are in rats.
Did Ostarine make rat bones stronger? In the studies above, some density and structure measures improved, but the mechanical strength tests did not show a significant improvement.
Why do bone studies record uterine and prostate weight? To check whether a compound acts on hormone sensitive tissues outside bone. Increases in both were reported.
Is Ostarine a licensed medicine? No. It is not licensed anywhere and is supplied in the UK strictly for laboratory research.
Sources
- Hoffmann DB et al. (2019). Evaluation of ostarine as a selective androgen receptor modulator in a rat model of postmenopausal osteoporosis. J Bone Miner Metab. PubMed 29785666
- Komrakova M et al. (2020). The selective androgen receptor modulator ostarine improves bone healing in ovariectomized rats. Calcif Tissue Int. PubMed 31531719
- Böker KO et al. (2023). Treatment of osteoporosis using a selective androgen receptor modulator ostarine in an orchiectomized rat model. Endocrine. PubMed 37378829
- Hoffmann DB et al. (2025). Effects of combined treatment with selective androgen and estrogen receptor modulators ostarine and raloxifen on bone tissue in ovariectomized rats. Calcif Tissue Int. PubMed 41134342
- Gao W et al. (2005). Selective androgen receptor modulator treatment improves muscle strength and body composition and prevents bone loss in orchidectomized rats. Endocrinology. PubMed 16099859
- Kearbey JD et al. (2007). Selective androgen receptor modulator (SARM) treatment prevents bone loss and reduces body fat in ovariectomized rats. Pharm Res. PubMed 17063395
- Narayanan R, Coss CC, Dalton JT (2018). Development of selective androgen receptor modulators (SARMs). Mol Cell Endocrinol. PubMed 28624515
- Dalton JT et al. (2011). The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women. J Cachexia Sarcopenia Muscle. PubMed 22031847
- Dobs AS et al. (2013). Effects of enobosarm on muscle wasting and physical function in patients with cancer. Lancet Oncol. PubMed 23499390
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