MK-677 vs MK-2866

The Dose Guy’s verdict

Oct 27, 2026
8 sources

Ostarine, the MK-2866 on the label, for most people. They do different jobs: ostarine works the androgen receptor and builds or holds muscle directly, while MK-677 raises your growth hormone and your appetite. If the goal is muscle, especially on a cut, ostarine is the pick and MK-677 would fight you every meal. MK-677 earns a place only on a bulk or for deeper sleep, and the bulk is the one place people sensibly run the two together.

Which would I take?Ostarine, and MK-677 only on a bulk.

How they differ

They pull different levers. Ostarine is a selective androgen receptor modulator, a SARM: it activates the receptor testosterone uses, mostly in muscle and bone, so what it adds is muscle. MK-677, sold as ibutamoren, is a growth-hormone secretagogue that works the hunger receptor: GH and IGF-1 climb, sleep deepens, appetite surges, and the early jump on the scale is mostly water.

That splits the costs too. Ostarine’s bill is hormonal: mild testosterone suppression by weeks six to eight, an HDL dip, and a rare liver injury, which is why it runs in 8 to 12 week cycles with no alcohol. MK-677 leaves your testosterone alone; its bill is metabolic: hunger, water, and a fasting glucose that creeps up. So a cut belongs to ostarine, and a bulk where you struggle to eat or sleep is the one place MK-677 helps.

Both are a daily pill, so the habit is the same and only the timing differs: ostarine once a day whenever suits you, MK-677 before bed. Both come from an unregulated market, so a third-party COA matters on either, and both are banned in tested sport.

What the research shows

No study puts them side by side, and they mostly measure different things. The closest overlap is lean mass in older adults, from different trials in different people:

No head-to-head trial of ostarine against MK-677 exists, and no trial has tested the two together.as of Aug 2026

In healthy older adults over 12 weeks, ostarine raised total lean body mass dose-dependently, significant for 3 mg versus placebo with p under 0.001, and improved physical function with p=0.013.J Cachexia 2011 · phase 2 RCT · n=120

At one year in healthy older adults, fat-free mass gained 1.1 kg on MK-677 versus a loss of 0.5 kg on placebo, and the gain did not improve strength or function.Annals 2008 · RCT · 2 yr · n=65

In healthy adults age 64 to 81 on MK-677 25 mg, fasting glucose rose from 5.4 to 6.8 mmol/L in four weeks.JCEM 1996 · dose-ranging · n=32

Both added lean mass in older adults, in two different trials: ostarine’s gain came with better function at a dose far below what the gym runs, and MK-677’s came with a glucose bill instead.

How people run them

Run ostarine at 15 to 20 mg a day for a first run, 8 to 12 weeks, protein high and training hard. Get bloodwork after the cycle; if testosterone is still flat a month out, a short PCT with nolvadex cleans it up. Take MK-677 at 10 to 15 mg before bed, hold there, and check fasting glucose early and every few weeks.

Switching rarely makes sense, because they do different jobs. The year’s shape is ostarine alone on the cut and ostarine plus MK-677 on the bulk, where the pair is common and not redundant. Add one at a time: ostarine first, MK-677 two weeks later, so when something goes wrong it has one suspect. Never stack them on a cut. MK-677 does nothing for testosterone recovery after an ostarine cycle, so it is no substitute for bloodwork or a PCT. Skip the alcohol for the whole ostarine run; your liver is already the thing to watch.

Ostarine15–20 mg/day8 to 12 weeks; plenty for a first run, and more mostly buys suppression.

MK-67710–15 mg nightlyPre-bed, so you sleep through the worst hunger; 25 mg is the trial ceiling.

The bulk stackboth, staggeredOstarine first, MK-677 two weeks later, so a side has one suspect.

After ostarinebloodwork, PCT if flatMK-677 does nothing for your testosterone recovery.

Side effects, side by side

Different bills: ostarine’s lands on hormones and the liver, MK-677’s on appetite and blood sugar:

commonMild testosterone suppression on ostarine, usually noticeable by weeks six to eight and usually recovered within a month of stopping. MK-677 does not suppress.

commonHunger and water on MK-677: appetite strongest in the first weeks, puffy hands, feet, and face. Both settle with time or a lower dose.

monitorHDL dips on ostarine. Run a lipid panel after the cycle and let it recover before the next one.

monitorFasting glucose rises on MK-677 and insulin sensitivity worsens. Check yours before and during.

monitorLiver injury is rare on ostarine but documented in healthy young men, and MK-677 has a case report of raised liver enzymes. Yellowing skin or eyes, dark urine, or just feeling off means stop and get liver enzymes checked.