Source comparison
MK-677 Pharmacokinetics: Parent Compound vs Metabolite Clearance
MK-677 operates as a ghrelin receptor agonist. It binds to GHSR1a receptors in the pituitary and hypothalamus, triggering endogenous growth hormone release in discrete pulses every 3–4 hours. The parent compound reaches peak plasma concentration 2–3 hours post
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- MK-677 operates as a ghrelin receptor agonist. It binds to GHSR1a receptors in the pituitary and hypothalamus, triggering endogenous growth hormone release in discrete pulses every 3–4 hours. The parent compound reaches peak plasma concentration 2–3 hours post-dose, then follows first-order elimination kinetics with a half-life of 4.7 hours (range 4.1–6.2 hours across published studies). Five half-lives. The standard threshold for 97% clearance. Puts parent compound elimination at 23.5–31 hours.
- But clearance isn't binary. MK-677 undergoes hepatic metabolism via CYP3A4 and CYP2D6, producing at least three measurable metabolites. The primary metabolite retains partial agonist activity at the ghrelin receptor, extending the biological effect window beyond what parent compound pharmacokinetics predict. Plasma assays using LC-MS/MS can detect these metabolites for 10–14 days post-dose at single-digit nanogram concentrations. Well below therapeutic thresholds but above detection limits for competitive testing panels.
- The second-order effect matters more for most users. MK-677-induced GH pulses elevate serum IGF-1 by 40–90% within 2–4 weeks of consistent dosing. IGF-1 has its own half-life of approximately 12–15 hours, but the hepatic production rate remains elevated for 14–21 days after stopping MK-677 because the signalling cascade reset isn't immediate. Blood work taken one week after your last dose will still show IGF-1 levels 20–40% above baseline. Not because MK-677 is still present, but because the downstream pathway it activated hasn't fully downregulated.