Raun K, Hansen BS, Johansen NL, et al. (1998). Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol, 139(5):552-61.
AnimalPMID 9849822DOI↩
What is ipamorelin?
Your stomach makes a hormone called ghrelin. It’s best known for making you hungry, but it also signals the pituitary gland to release growth hormone. Ipamorelin is a lab-made peptide, just five amino acids long, that mimics this signal by activating the same receptor [1, 2].
Ipamorelin was developed by the drug company Novo Nordisk in the 1990s. When it was introduced in 1998, scientists called it the first selective growth hormone releaser, for reasons explained below [1]. It was later tested in hospital patients recovering from bowel surgery, but development was stopped after disappointing trial results [S1].
Today ipamorelin isn’t part of any FDA-approved drug. It’s increasingly marketed by medical spas and wellness clinics for weight loss, anti-aging, sleep, and bodybuilding [S1].
How does it work?
- A burst of growth hormone. In healthy volunteers given ipamorelin by IV, growth hormone rose in a single burst that peaked about 40 minutes later, then faded. Ipamorelin itself was cleared from the blood with a half-life of about 2 hours [3].
- What makes it “selective.” In pigs, two older growth hormone–releasing peptides (GHRP-6 and GHRP-2) also raised the stress hormones ACTH and cortisol. Ipamorelin didn’t, even at doses more than 200 times higher than needed to release growth hormone. It also left other pituitary hormones unchanged [1].
- Effects on the gut. Because ghrelin also helps move food through the digestive system, researchers tested ipamorelin as a way to get the gut working again after surgery [2].
What has research found?
In animals
- Gut recovery after surgery: In rats that had abdominal surgery, ipamorelin shortened the time to the first bowel movement. Repeated doses also increased eating and weight gain [2]. It also sped stomach emptying after surgery [4].
- Bone: In female rats, ipamorelin increased the rate at which bones grew longer [5]. Over 12 weeks, it also increased bone mineral content, mainly because the bones grew larger, not denser [6]. It also counteracted the loss of muscle strength and bone formation caused by steroid medicines [7].
- Pain: In rats, it reduced pain sensitivity in both the gut and the paws [8].
- Chemotherapy weight loss: In ferrets given the chemotherapy drug cisplatin, ipamorelin reduced weight loss by about 24% [9].
- A surprise: In mice, ipamorelin increased body fat, through a route that didn’t involve growth hormone and may have involved eating more [10]. That’s worth knowing, given that it’s marketed for fat loss.
In people
- How the body handles it: In 40 healthy men given different doses by IV, ipamorelin triggered growth hormone release at every dose [3].
- Recovery after bowel surgery: In a placebo-controlled trial of 117 patients, ipamorelin given by IV twice daily for up to a week was well tolerated. Patients on ipamorelin tolerated their first solid meal about 7 hours sooner than those on placebo (25.3 versus 32.6 hours), but the difference wasn’t statistically significant [11]. Development was discontinued after this result [S1].
- Everything else: No published trials have tested ipamorelin for growth hormone deficiency, anti-aging, fat loss, or muscle building. FDA found the evidence for any medical use limited, with no data at all for injections under the skin, the way it’s usually sold [S1].
How strong is the evidence?
| What we know so far | What we still don’t know |
|---|---|
| It reliably triggers growth hormone release in animals and people [1, 3] | Whether that leads to any benefit for muscle, fat, aging, or sleep, because none of these have been tested in people [S1] |
| It was selective in animal tests, with no stress-hormone spike [1] | Long-term safety, because animal toxicity studies are too limited [S1] |
| It was well tolerated for up to a week in a surgical trial [11] | The right dose, how often, or for how long [12] |
| It improved gut movement and bone in animal studies [2, 6] | Whether those animal results apply to people |
A few more things to keep in mind:
- The one completed patient trial missed its goal [11].
- Most early research came from the companies developing it. Novo Nordisk ran the early studies [1, 5], and later gut research included scientists from the drug company Helsinn [4].
- Popular combinations are untested in people. The common pairing of CJC-1295 with ipamorelin has only been studied in mice [12].
Safety: what we know
- In the surgical trial, side effects were common in both groups: 87.5% of patients on ipamorelin and 94.8% on placebo had at least one [11]. These were people recovering from major surgery, so some side effects are expected.
- Concerns FDA has raised: Two patients who received ipamorelin in that trial died. FDA noted it’s unclear whether ipamorelin was the cause, but flagged the deaths, along with higher rates of low potassium and high blood sugar, as safety concerns [S1].
- Other possible effects: Because ipamorelin acts on the ghrelin receptor, FDA reviewers noted it might have addictive properties and could affect reproductive health and pregnancy, and that animal safety studies are too limited to say [S1].
- Immune reactions: FDA warns that impurities and clumping in injected ipamorelin could trigger immune reactions, and that its unusual, non-natural amino acids make quality harder to check [S2].
- Black-market products: Anti-doping and forensic labs have found altered versions of ipamorelin, with an extra amino acid added, in seized products [13, 14]. A 2026 review warns that peptides from the unregulated supply chain are often mislabeled or contaminated [15].
- Growth hormone–related effects: Reported side effects of this family of peptides include hormone and blood sugar changes, fluid retention, joint and muscle pain, and injection-site reactions [16].
Legal status
- Not an approved medicine. It isn’t part of any FDA-approved drug [S1]. Its development was stopped before it could be approved [S1].
- United States: FDA lists ipamorelin among substances that may pose significant safety risks in compounding [S2]. In October 2024, FDA’s advisory committee voted 12 to 0, with one abstention, against letting pharmacies use it to make compounded drugs [S3].
- Sports: Banned at all times by the World Anti-Doping Agency (WADA) [S4].
The bottom line
Ipamorelin is an elegant piece of drug design: a growth hormone trigger that, in animals, left stress hormones alone. Animal studies hinted at benefits for gut recovery and bone.
But its one large patient trial didn’t meet its goal, development stopped, and both FDA and its expert advisers have raised safety concerns. The wellness uses it’s marketed for today, from anti-aging to fat loss, have never been tested in people. Whether its unusual selectivity could still be put to good use is an open question that future research could revisit.