MK-677

MK-677 (Ibutamoren, originally coded MK-0677 by Merck) is an orally active growth hormone secretagogue. Unlike the injectable GHRPs (ipamorelin, GHRP-2, GHRP-6), it is not a peptide at all: it is a small non-peptide molecule engineered to survive digestion and mimic ghrelin. It is grouped with the peptide secretagogues because it acts on the same target and raises growth hormone the same way, just from a pill or a swallow of solution instead of a subcutaneous injection.

The molecule binds the growth hormone secretagogue receptor (GHS-R1a), the ghrelin receptor, in the pituitary and hypothalamus. Receptor activation triggers a pulse of growth hormone and, downstream in the liver, a sustained rise in insulin-like growth factor 1 (IGF-1). Its defining pharmacological trait is a long half-life of roughly 24 hours, which is why a single daily dose keeps GH pulses and IGF-1 elevated around the clock, something the short-acting injectable GHRPs cannot do without multiple shots per day.

The strongest human data comes from a 2008 Annals of Internal Medicine trial by Nass and colleagues. Healthy older adults taking 25 mg of MK-677 daily for one year raised GH and IGF-1 into the range of healthy young adults and gained roughly 1.1 kg of lean body mass versus placebo. Earlier work by Murphy (1998) showed MK-677 reversed the catabolic protein loss caused by dietary restriction, and Copinschi (1997) documented improved sleep architecture, specifically increased stage 4 (deep) and REM sleep, after just one week of dosing.

Because MK-677 is oral and long-acting, the fasting rules that dominate injectable GHRP use are far less strict: you do not need to time it around an empty stomach the way you do with a 15-minute-half-life peptide. Many users take it before bed to align the GH pulse with natural overnight secretion and to sleep through the mild drowsiness it can cause. The practical measurement question with research liquid is volume, not injection: a 25 mg/mL solution means a 25 mg dose is 1 mL drawn on an oral or insulin syringe, which is what the calculator above computes.

The side effect profile follows directly from elevated GH and IGF-1. Increased appetite is common and often pronounced (the ghrelin receptor is the hunger receptor), as is water retention and a puffy or fuller look in the first few weeks. The more important concern is metabolic: MK-677 can raise fasting blood glucose and reduce insulin sensitivity, so anyone with prediabetes or diabetes should monitor closely. It is not FDA-approved for any indication, was investigated but never brought to market for GH deficiency and frailty, and is prohibited in competition by WADA.