MK-0773
Also known as: MK-0773, MK0773
The SARM that got furthest — Merck took it to phase 2 in older women. It worked, and it was stopped for liver signals.
Substance family
Non-steroidal compounds binding the same androgen receptor as testosterone, but favouring muscle and bone over prostate and hair. The selectivity is real; the suppression of the body's own production is not avoided by it. None is approved anywhere.
Effects on
Which outcomes this substance acts on — descriptive, not a recommendation.
Strain profile
Where this substance is most likely to hit — a rough orientation, individually dependent on dose, duration and predisposition.
This substance causes
Dosing & protocols by goal
Rough orientation ranges as reported in harm-reduction literature — not an individual treatment plan. Doses are individual and open-ended; frequency depends on the ester or half-life.
Clinical trials (dose range studied)
MedicalDose
50 mg twice daily in the phase 2 trial
Frequency
2× daily
Cycle length
6 months
Studied in older women with sarcopenia. Lean mass increased significantly against placebo — one of the few SARMSARMA non-steroidal compound that binds the androgen receptor with claimed tissue selectivity. efficacy results demonstrated in humans over months rather than weeks.
Grey market practice
Not a recommendationDose
Not meaningfully available
Frequency
—
Cycle length
—
MK-0773 is essentially absent from the grey market. Anything sold under this name should be treated as unverified.
Side effect & countermeasure
Typical problems and what you can do to reduce harm — at a glance. Does not replace medical monitoring.
Problem
It is steroidal, despite the SARM label
Countermeasure
Like YK-11, MK-0773 has a steroid backbone rather than the non-steroidal structure that defines most of this category. The 'SARMSARMA non-steroidal compound that binds the androgen receptor with claimed tissue selectivity.' designation here refers to the selective tissue profile, not to the chemistry. It is a useful reminder that the label describes an intended behaviour, not a chemical class.
Problem
Liver enzyme elevations ended the programme
Countermeasure
The phase 2 trial showed the compound working — and also showed transaminase elevations in a portion of participants. Combined with the regulatory environment for muscle-wasting drugs, that ended development. It is the second major SARMSARMA non-steroidal compound that binds the androgen receptor with claimed tissue selectivity. programme stopped for the same organ.
Problem
Suppression in women too
Countermeasure
The trial was in postmenopausal women, where suppressionsuppressionThe body shutting down its own testosterone production because an external source is present. of endogenous androgens is a different question than in men. In a man, an androgen receptorandrogen receptorThe docking site in the cell that androgens bind to in order to have any effect. agonist at an effective dose suppresses the axis — that applies here as to any other.
Problem
Anything sold under this name is questionable
Countermeasure
Since the compound never reached the market and is not manufactured for the grey market at scale, products labelled MK-0773 are more likely to contain something else. That is a general SARMSARMA non-steroidal compound that binds the androgen receptor with claimed tissue selectivity. problem and an acute one here.
Overview
MK-0773 is the SARM that came closest to being a real medicine, and almost nobody talks about it because it is not for sale.
Merck developed it for sarcopenia — the loss of muscle mass with age. It reached a phase 2 trial in older women with muscle loss, dosed at 50 mg twice daily for six months. That is a far longer and more rigorous human exposure than any other compound in this category has had.
What the Trial Found
It worked. Lean body mass increased significantly compared with placebo over six months, which is a genuine efficacy result in humans — the thing that every SARM is claimed to do and that almost none has actually demonstrated in a proper trial.
It also produced elevations in liver transaminases in a portion of participants. Development was discontinued.
The Pattern Worth Noticing
Read this page alongside GSK-2881078 and a pattern emerges that is more informative than any individual compound page here.
Two large pharmaceutical companies took SARMs into serious human trials. Both compounds demonstrated real muscle-building effects. Both programmes were stopped after liver enzyme elevations appeared.
Meanwhile, the compounds people actually buy — ostarine, LGD-4033, RAD-140, and the second-tier ones like S-23 and LGD-3303 — have either less human data or none at all. Their reputation for being gentle rests on the absence of investigation, not on findings of safety.
That is the single most useful thing this section of the site can convey. When the class was studied properly, the liver is where the problems showed up. That is also consistent with the elevated liver values users of ostarine and RAD-140 report.
A Note on the Chemistry
MK-0773 has a steroidal backbone. So does YK-11. Both are sold or discussed under the SARM label, which describes an intended tissue-selectivity profile rather than a chemical class.
This matters for anyone whose reason for choosing SARMs was "not a steroid". That reasoning does not survive contact with the actual chemistry in at least two cases in this category.
Side Effects & Risks
- Elevated liver transaminases — documented in the phase 2 trial
- Suppression of the body's own production in men
- Limited public safety data beyond the trial results
- Products sold under this name are unlikely to be genuine
Blood Work & Monitoring
- Liver values (ALT, AST, GGT, bilirubin) — the finding that ended development
- Total and free testosterone, LH, FSH
- Lipid profile (LDL, HDL, triglycerides)
Legal status by region
Regulation differs considerably between jurisdictions and changes over time. This is a rough orientation, not legal advice — check the rules that apply where you are.
| Region | Regulatory status |
|---|---|
| United States | Not approved; development discontinued |
| EU / UK | No marketing authorisation |
| Most other jurisdictions | Unregulated; rarely encountered |
| Competitive sport | Prohibited at all timesListed by WADA under S1. |