MK-677 is an oral, small-molecule drug developed by Merck that mimics ghrelin to raise growth hormone and IGF-1. It is not actually a peptide, but sits on the same GH-axis "stack." Multiple phase 2 trials ran for frailty and hip-fracture recovery; all were halted, partly over insulin-resistance signals. It is banned at all times by WADA.
Ipamorelin is a synthetic peptide that nudges the pituitary to release growth hormone. It was trialled by pharma for post-operative ileus, failed to win approval and was dropped. Today it is sold only as a research chemical and used off-label in wellness clinics — and it is banned at all times in tested sport by WADA.
Both peptides share an evidence grade of C. The right choice depends less on the data and more on what you're trying to do — MK-677 for gh-deficient adults (trialled), Ipamorelin for post-operative ileus (trialled).
Murphy et al. 1998 showed MK-677 reversed protein catabolism in healthy volunteers on a calorie-restricted diet. Several phase 2 programmes followed in GH-deficient adults; none progressed to approval.
The one indication ipamorelin reached human trials for. A randomised, placebo-controlled phase 2 study in bowel-resection patients (Beck et al. 2014) reported some signal on gastric motility but missed its primary endpoint. Development was halted.
Reliably raises GH in animals and healthy volunteers in short-duration studies. Whether sustained micro-pulses translate to meaningful long-term clinical outcomes in humans is not established.
The most important real-world finding from the human trials is impaired insulin sensitivity: fasting glucose and HbA1c rose meaningfully in healthy older adults on chronic dosing (Nass et al. 2008), and the effect was large enough that it would push some users into a pre-diabetic range. This is not a vendor scare-story — it is a phase 2 trial result. Other consistently reported effects include water retention, increased appetite, transient muscle aches and mild lethargy. In the frail elderly, the Adunsky hip-fracture trial reported serious adverse events including congestive heart failure signals — part of why that programme was halted. Long-term tumour risk via sustained IGF-1 elevation is a theoretical concern (IGF-1 is mitogenic) and a reason for caution in anyone with active cancer or a cancer history. Products sold as "MK-677" or "Nutrobal" outside the trials are unregulated; purity, dose accuracy and contamination are real risks.
In short-duration human trials ipamorelin was generally well tolerated, with the most common reports being injection-site reactions, mild headache and transient flushing. Longer-term safety in healthy adults using it for performance or anti-ageing reasons is unknown — there are no multi-month controlled trials in this population. Chronic stimulation of the GH/IGF-1 axis is the main theoretical concern: it could in principle worsen insulin resistance, drive water retention, accelerate diabetic retinopathy, or promote the growth of pre-existing tumours (IGF-1 is mitogenic). People with active cancer, a cancer history, diabetes, or who are pregnant or breastfeeding should not use it. Products sold as "ipamorelin" online are unregulated research chemicals — purity, sterility and dose-per-vial vary, and contamination is a real risk.
Both peptides share an evidence grade of C. The right choice depends less on the data and more on what you're trying to do — MK-677 for gh-deficient adults (trialled), Ipamorelin for post-operative ileus (trialled).
Pepwyse comparison pages are generated from the same structured data behind each peptide profile. Want a different head-to-head? Use the compare picker or ask MK-677 directly via the Ask-Peppy button. Not medical advice — see how we grade evidence.