Ostarine (MK-2866) and Stenabolic (SR-9009) are often listed together, but they are not the same kind of compound. Ostarine is a selective androgen receptor modulator. Stenabolic is a Rev-ErbA agonist that has nothing to do with the androgen receptor at all. Comparing them is still useful, because the contrast shows how differently two research compounds can work and how different the quality of their evidence is.
Two different mechanisms
Ostarine binds the androgen receptor in muscle and bone and switches on the same anabolic signalling that testosterone does, with far less activity in the prostate and skin. Its effects are on protein synthesis, lean mass and bone density.
Stenabolic binds Rev-ErbA alpha and beta, two nuclear receptors that sit inside the circadian clock machinery. Activating them shifts the expression of genes involved in mitochondrial biogenesis, fatty acid oxidation and glucose handling. In the original 2012 study from the Scripps Research Institute, mice given SR-9009 ran further, lost fat and showed lower cholesterol and inflammation markers, all without any change in muscle mass. The effect is metabolic, not anabolic.
The evidence gap
This is the biggest difference between the two. Ostarine has phase I, II and III human trials with well over a thousand participants exposed. Stenabolic has never been given to a human being in a published study. Everything known about it comes from rodents and cell cultures. The compound also has a serious pharmacokinetic problem: its oral bioavailability in mice was very low and its half-life very short, which is why the Scripps team delivered it by injection. Whether oral SR-9009 reaches meaningful blood levels is an open question that the literature has not answered.
What each compound was measured to do
| Ostarine (MK-2866) | Stenabolic (SR-9009) | |
|---|---|---|
| Receptor | Androgen receptor | Rev-ErbA alpha and beta |
| Human data | Phase I to III trials | None published |
| Main measured effect | Lean mass and stair climb power (12 weeks, humans) | Endurance, fat mass and lipids (rodents) |
| Hormonal effect | Mild, reversible testosterone reduction | None on the gonadal axis in rodents |
| Half-life | About 24 hours | Under 4 hours (rodent) |
| Oral bioavailability | Good | Poor |
Why the two get paired
The pairing appears in online logs because the mechanisms do not overlap: one compound is anabolic and one is metabolic, and Stenabolic does not add to the hormonal suppression that Ostarine causes. That logic is sound as far as it goes, but it rests on one compound with human data and one without. There is no study of the combination and no human study of Stenabolic on its own. Our fat loss guide and stacks guide set out the research position on both.
Products
We stock Ostarine MK-2866 10mg and Stenabolic SR-9009 8mg, both 90 capsules from Dexterz Labs and both independently batch tested, with certificates on the lab results page. For a compound with a similar metabolic profile and rather more human data, see the guide to Cardarine.
All products on this site are sold for laboratory research use only and are not for human consumption. Nothing in this article is medical advice.