MK-677 (Ibutamoren)

Key points

• MK-677 (ibutamoren) is a small molecule taken by mouth, not a peptide, SARM or steroid.
• It raises the body's own growth hormone and IGF-1 by acting on the ghrelin receptor.
• It has been through several human trials but was never approved, partly because of its effects on blood sugar and a heart concern in one trial.
• It has no UK marketing authorisation, and it is prohibited in sport at all times.

Quick facts

What it is

Oral growth hormone secretagogue (small molecule, not a peptide)

Studied for

Raising growth hormone; lean mass

UK status

Not a licensed medicine; sold for research use

Human evidence

Several trials; raises IGF-1, limited clinical benefit

In sport

On the WADA Prohibited List

How it works

MK-677 binds the ghrelin receptor, the same one the hunger hormone uses, and this prompts the pituitary to release growth hormone, which in turn raises IGF-1 in the liver. Taken as a daily tablet, it tends to enlarge the body's natural growth hormone pulses rather than flood the system, which is why its effects are gentler than injected growth hormone.

What the evidence shows

Unusually for this field, MK-677 has several placebo controlled human trials, from a week up to two years, though mostly in small groups. A long trial in healthy older adults found a modest gain in lean mass but no improvement in strength or everyday function. Trials in hip fracture recovery and in Alzheimer's disease did not show a clear clinical benefit despite raising IGF-1. So it reliably moves the hormone numbers, but the real world payoff is far less clear.

What it does not settle

• Whether any benefit is worth the effects on blood sugar is not settled.
• Long term safety, and any cancer risk from sustained higher IGF-1, are not established.
• It has not been compared head to head with other growth hormone treatments.

Side effects

Common

• A marked increase in appetite, which was the most common effect in trials.
• Mild, temporary swelling in the lower legs and muscle aches.
• Raised fasting blood sugar and reduced insulin sensitivity, so it can worsen glucose control.

Less common but serious

• A trial in older adults recovering from a hip fracture was stopped early after a possible signal of heart failure.
• People with diabetes or prediabetes, heart problems, fluid retention or a history of cancer need particular caution, and it is not for use in pregnancy or under 18.

Report any suspected side effect through the MHRA Yellow Card scheme.

UK legal status and access

MK-677 has no UK marketing authorisation, so it is not a licensed medicine and is not offered by registered clinics or pharmacies. It is sold online labelled for research use. Testing has found products that did not contain what the label claimed, so the stated strength of any such product cannot be relied on.

Common questions