MK-677 vs Ipamorelin
Research Comparison

Research Overview

MK-677 vs ipamorelin compares two agonists of one receptor. Both act at the growth hormone secretagogue receptor (GHS-R1a), whose natural ligand is ghrelin, an acylated 28-residue stomach peptide (Kojima et al., 1999). The difference is chemistry. MK-677, also written MK 677 and named ibutamoren, is an orally active non-peptide that Merck described in 1995 as L-163,191, or MK-0677 (Patchett et al., 1995). Ipamorelin is a synthetic pentapeptide that Novo Nordisk scientists described in 1998 as the first selective growth hormone secretagogue (Raun et al., 1998).

So ibutamoren vs ipamorelin is a question of class, which shapes route, duration, hormone selectivity and the human record. Disguised Alpha supplies MK-677 as 10MG capsules, 60 per bottle, and ipamorelin as a lyophilized powder, both for laboratory research use only. Nothing on this page is guidance for use in people.

Structure and Class

MK-677 is a spiropiperidine small molecule: an N-methanesulfonyl spiro(indoline-3,4'-piperidine) core joined by amide bonds to O-benzyl-D-serine and 2-aminoisobutyric acid (Aib). The product page lists C27H36N4O5S and 528.7 g/mol, matching the ibutamoren free base (PubChem CID 178024). The trial papers name the mesylate salt (Adunsky et al., 2011), C28H40N4O8S2, 624.8 g/mol; the lot certificate is the place to confirm which form the capsules hold.

Ipamorelin is Aib-His-D-2-Nal-D-Phe-Lys-NH2, from a series lacking the central Ala-Trp dipeptide of GHRP-1 (Raun et al., 1998). The product page lists C38H49N9O5, 711.86 g/mol, matching PubChem CID 9831659.

Both carry an Aib unit at the free amino end and D-configured aromatic side chains, but PubChem counts two hydrogen-bond donors on ibutamoren against eight on ipamorelin. When Novo Nordisk sought oral secretagogues from the ipamorelin lead, its chemists shrank the molecule and cut its hydrogen-bonding potential, and most new compounds reached oral bioavailability of 10 to 55 percent in dogs (Hansen et al., 1998). Per milligram, MK-677 free base holds about 1.35 times as many molecules as ipamorelin.

Side by Side

Research Context: MK-677

In rat pituitary cells, Merck found MK-677 acted like GHRP-6, not growth hormone releasing hormone (GHRH), with an EC50 of 1.3 nM. In dogs given it by mouth, aldosterone, LH, thyroxine and prolactin did not change significantly and cortisol rose only modestly (Patchett et al., 1995). In beagles, one oral exposure raised peak growth hormone up to 15.8 fold and kept it elevated up to 360 minutes, a duration the authors contrasted with GHRP-6; IGF-I was 30 percent higher at 480 minutes and cortisol rose 2.4 fold (Jacks et al., 1996).

In a placebo-controlled trial in 32 healthy adults aged 64 to 81, two weeks of once-daily oral MK-677 at the highest of three amounts raised mean 24-hour growth hormone 97 percent by enlarging existing pulses, and IGF-I rose. Fasting glucose rose, cortisol did not change, and prolactin rose 23 percent but stayed within the normal range (Chapman et al., 1996).

A two-year randomized trial in 65 healthy adults aged 60 to 81 found fat-free mass up against placebo while visceral fat, strength and function did not differ; fasting glucose and cortisol rose, insulin sensitivity fell, and increased appetite, mild leg swelling and muscle pain were the most frequent side effects (Nass et al., 2008).

In 563 people with mild to moderate Alzheimer's disease, 12 months of MK-677 raised IGF-1 about 73 percent without slowing progression (Sevigny et al., 2008). A phase IIb trial in 123 older adults after hip fracture was terminated early after a congestive heart failure signal in a few participants (Adunsky et al., 2011), and a 2025 case report described raised liver enzymes, which returned to normal, in a man who had used MK-677 for two months (Cobani et al., 2025).

MK-677 did not become an approved drug, and FDA's list of bulk drug substances that may present significant safety risks places ibutamoren mesylate in compounding category 2 under sections 503A and 503B, citing the potential for congestive heart failure. The MK-677 research guide covers later pediatric work under the code LUM-201.

Research Context: Ipamorelin

Ipamorelin released growth hormone from primary rat pituitary cells with potency similar to GHRP-6 (EC50 1.3 nM), acted through a GHRP-like receptor rather than the GHRH receptor in antagonist profiling, and released growth hormone in anesthetized rats and conscious swine. In swine, none of the secretagogues tested changed FSH, LH, prolactin or TSH. GHRP-6 and GHRP-2 raised ACTH and cortisol, but ipamorelin did not raise either beyond the levels seen with GHRH, even at more than 200 times its ED50 for growth hormone release (Raun et al., 1998).

In healthy men given 15-minute intravenous infusions at five escalating rates, ipamorelin showed proportional kinetics, a terminal half-life of about two hours and a single growth hormone episode peaking near 40 minutes (Gobburu et al., 1999). That study measured only ipamorelin and growth hormone, so the selectivity data cited here come from swine.

A double-blind, placebo-controlled phase 2 trial in 114 adults after bowel resection used intravenous infusions for up to seven days. Adverse events were recorded in 87.5 percent of the ipamorelin group and 94.8 percent on placebo, and the key and secondary efficacy analyses showed no significant difference (Beck et al., 2014).

No ipamorelin drug has been approved. On the same FDA list, ipamorelin acetate sits in category 2 under section 503B; FDA cites possible immunogenicity for certain routes, its unnatural amino acids and a published study reporting serious adverse events, including death, with intravenous ipamorelin for gastric motility. More is in the ipamorelin research guide.

Choosing Between Them for a Research Question

Choose by chemistry and exposure profile. Oral exposure, sustained once-daily stimulation, small-molecule pharmacology at GHS-R1a, or designs that track glucose and insulin beside growth hormone have precedent with MK-677. Short single-episode release, selectivity against ACTH and cortisol, or intravenous kinetics have precedent with ipamorelin.

Both act at one receptor, so they are not a complementary pair the way a GHRH analog and a secretagogue are; the CJC-1295 vs Ipamorelin and Tesamorelin vs Ipamorelin comparisons cover that kind of pairing. A PubMed search in October 2026 found no study testing MK-677 and ipamorelin side by side. A head-to-head design would need equimolar amounts, sampling fitted to each profile, and cortisol, prolactin, glucose and insulin readouts, since that is where the published profiles diverge.

Handling and Storage

MK-677 capsules ship sealed, and the product page lists 15 to 25°C in the original container, away from moisture and direct light. Ipamorelin ships as a lyophilized powder, and its page lists -20°C as shipped and 2 to 8°C after reconstitution, protected from light, with freeze/thaw cycles avoided. Let the vial reach room temperature before opening, add diluent gently down the wall, and split stock into single-use aliquots.

For both, record the lot number and keep its certificate from the COA portal. Where an MK-677 certificate reports measured content per capsule, use that value, and base molar calculations on the form the certificate names: 528.7 g/mol for the free base or 624.8 g/mol for the mesylate. For ipamorelin, use the measured net peptide content; the IP01 certificate reports 10.58 mg against a 10 mg label.

Questions Researchers Ask

MK-677 vs ipamorelin: what is the difference?

Both are ghrelin receptor agonists. MK-677 (ibutamoren) is an orally active small molecule (Patchett et al., 1995); ipamorelin is a five-residue synthetic peptide (Raun et al., 1998) with a terminal half-life of about two hours after intravenous infusion in volunteers (Gobburu et al., 1999).

Ibutamoren vs ipamorelin: which is more selective?

On the published data, ipamorelin, with a caveat. In swine it did not raise ACTH or cortisol beyond GHRH levels and left prolactin unchanged (Raun et al., 1998), while MK-677 raised cortisol modestly in dogs (Jacks et al., 1996) and prolactin by 23 percent, within the normal range, in older adults (Chapman et al., 1996). The species differ, and no PubMed-indexed study compares them directly.

Is MK-677 a peptide like ipamorelin?

No. MK-677 is a spiroindoline sulfonamide small molecule (Jacks et al., 1996), designed as a mimetic of the growth hormone releasing peptides (Chapman et al., 1996). It is grouped with peptides because it acts at the ghrelin receptor. Ipamorelin is a true pentapeptide.

Ipamorelin vs MK-677: are they approved or prohibited?

Neither is an approved drug, and FDA lists both in category 2 of its compounding interim policies. The 2026 WADA Prohibited List names ibutamoren (MK-677) and ipamorelin as growth hormone secretagogues in section S2.2.4, prohibited at all times.