Ipamorelin explained: the growth hormone peptide that leaves stress hormones alone

• What it is: a five-amino-acid peptide from a Novo Nordisk drug-discovery program, with three building blocks that aren't standard amino acids [1].
• Why it matters: growth hormone up, without the cortisol and ACTH bump older peptides caused — even at 200× the amount needed [1].
• In people: a study in 40 healthy men saw one clean pulse of growth hormone peaking at about 40 minutes, with a half-life of about 2 hours [2].
• The catch: its one big trial in patients missed its main goal [5], and it has never been approved as a medicine.

Ipamorelin came out of a big chemistry program at Novo Nordisk in Denmark. The team was working through a family of growth hormone–releasing peptides (GHRPs) and landed on a five-amino-acid design that released growth hormone about as strongly as GHRP-6, a well-known peptide in that family [1].

Its sequence is Aib–His–D-2-Nal–D-Phe–Lys–NH2. Three of those five aren't standard amino acids: Aib, D-2-Nal and D-Phe, the mirror-image form of phenylalanine. Molecular weight: about 712.

It's a ghrelin mimic. Ghrelin is best known as the “hunger hormone,” but it also tells the pituitary to release growth hormone. Ipamorelin works through the same receptor [5][6].

Older peptides in this family, like GHRP-6 and GHRP-2, did release growth hormone. But they also pushed up ACTH and cortisol, the body's stress-hormone pair [1].

When Novo Nordisk's team tested ipamorelin in pigs, it matched GHRP-6 on growth hormone. ACTH and cortisol, though, stayed where they were with GHRH, the body's own growth hormone signal — even at more than 200 times the amount needed to release growth hormone. It also left FSH, LH, prolactin and TSH alone. The authors called the result very surprising [1].

That's why ipamorelin is known as the first selective growth hormone secretagogue, the title of the 1998 paper that introduced it [1].

• Power. In rat pituitary cells, it released growth hormone about as potently as GHRP-6 [1].
• Bone growth. In rats, leg bones grew faster — from 42 to 52 micrometers a day at the highest level tested, about 24% faster, in 15 days [3].
• Bone mineral. Over 12 weeks in adult female rats, bone mineral content went up — because the bones grew bigger, not denser [4].
• Gut recovery. In rats recovering from abdominal surgery, it got the gut moving sooner, and over two days it increased food intake and weight regain [6].
• In people. In 40 healthy men, each infusion produced a single pulse of growth hormone that peaked at about 40 minutes and then faded, with a half-life of about 2 hours [2].

The human record is thin. There's the study in healthy volunteers [2], and one Phase 2 trial in 114 people recovering from bowel surgery. That trial found it well tolerated, but it didn't beat placebo: the median time to a first solid meal was 25.3 hours versus 32.6 hours, a gap too small to count statistically [5].

It has never been approved as a medicine, and a 2026 sports-medicine review notes that rigorous human safety data for peptides like this are scarce [7]. We supply it for laboratory research only.

Ipamorelin has three non-standard building blocks. Get one wrong and you have a different molecule that can still look like a clean white powder. So before any batch goes on sale, an outside lab checks:

• Identity by mass spectrometry. The molecule's measured mass has to match ipamorelin.
• Purity by HPLC. How much of the vial is that one molecule — the exact figure for the lot, to two decimals. Never “99%+.”

Every ipamorelin batch we've released is on the ipamorelin lab-reports page, with its signed certificate. If a vial doesn't match its report, test it at any lab you like and we'll refund it in full.

Ipamorelin earned its reputation in one experiment: growth hormone on, stress hormones not. The animal work on bone and gut is interesting, the human data are thin, and the one big patient trial came up short. For the other side of the growth hormone system — the GHRH side — read our tesamorelin guide.