IGF-1 LR3 is a modified version of insulin-like growth factor-1, originally built as a cell-culture reagent to grow cells in the lab. It is not an approved medicine anywhere as IGF-1 LR3. It is heavily diverted into bodybuilding, where it carries real risks of hypoglycaemia, a biologically plausible cancer-signal concern, and acromegaly-like effects with chronic use. Banned at all times by WADA under S2.3.
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.
MK-677 sits at grade C; IGF-1 LR3 at grade D. On evidence alone, MK-677 is the safer recommendation. That said, "stronger evidence" doesn't always mean "right for you", read both pages, then talk to a clinician.
The intended, validated use. LR3 IGF-I is used in serum-free mammalian cell culture (CHO, HEK293) to support growth and recombinant protein production, at concentrations roughly 200× lower than insulin (Voorhamme & Yandell 2006). This is laboratory science; it is not a human use.
The reason it is sold. There are no controlled human trials of IGF-1 LR3 for muscle growth in healthy adults. The anabolic rationale is biologically plausible, IGF-1 signalling drives muscle protein synthesis, but plausible mechanism is not the same as proof of net benefit, and the safety profile (below) is the entire issue.
Frequently claimed online. No controlled human data in either direction. Often stacked with GH secretagogues; the combined safety profile of those stacks has never been studied.
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.
IGF-1 LR3 has one of the most concerning safety profiles of any peptide in this directory, with three distinct categories of risk. First, acute hypoglycaemia. IGF-1 and insulin receptors are structurally related, and IGF-1 has measurable affinity for the insulin receptor. The LR3 modifications produce a longer-acting, IGFBP-resistant analogue that can drive blood glucose down, sometimes hours after an injection, sometimes overnight, often unexpectedly. Severe hypoglycaemia is a real acute risk and the most common reason users present to hospital. Even the approved native IGF-1 drug (mecasermin) requires patients to eat shortly before or after every dose, and lists hypoglycaemia as a primary adverse reaction. Second, a biologically plausible cancer signal. Large epidemiology, Renehan et al. 2004 Lancet meta-analysis, and follow-up work synthesised by Pollak in Nature Reviews Cancer, has repeatedly associated higher circulating IGF-1 with increased risk of prostate, premenopausal breast and colorectal cancers. Causation is not proven, but the mechanism (IGF-1R signalling promotes cell proliferation and inhibits apoptosis) is biologically plausible. Chronic, supraphysiological exposure from an IGFBP-resistant analogue is exactly the exposure pattern that concern was raised about. Third, acromegaly-like effects. Chronically elevated IGF-1, the downstream driver of growth hormone, produces the same constellation seen in acromegaly: jaw and brow bone overgrowth, soft-tissue thickening, organ enlargement, insulin resistance, and cardiovascular remodelling. These changes accumulate slowly and some are not reversible. Fourth, quality control is absent. Vials sold as "IGF-1 LR3" are unregulated research-chemical material. Identity, purity, sterility, dosing accuracy and endotoxin content are not guaranteed and have repeatedly failed independent testing in adjacent peptide markets. If you have a personal or family history of cancer, diabetes, pre-diabetes, or cardiovascular disease, or are pregnant, breastfeeding or under 25, IGF-1 LR3 is a particularly poor choice.
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.
MK-677 sits at grade C; IGF-1 LR3 at grade D. On evidence alone, MK-677 is the safer recommendation. That said, "stronger evidence" doesn't always mean "right for you", read both pages, then talk to a clinician.
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.