Ipamorelin

1990-1996

The Selectivity Problem

GHRPs With Unwanted Effects

By the mid-1990s, growth hormone releasing peptides were well established. GHRP-6, GHRP-2, and Hexarelin could all trigger powerful growth hormone release. But they came with baggage.

These peptides also released cortisol (the stress hormone), prolactin, and sometimes aldosterone. They could cause intense hunger. For therapeutic use, these side effects were problematic. Doctors wanted to boost growth hormone, not stress hormones.

Researchers at Novo Nordisk set out to design a cleaner GHRP — one that would release growth hormone selectively, without disturbing other hormones.

1996-1999

Engineering Selectivity

Finding the Clean Molecule

Novo Nordisk's team systematically modified GHRP structures. They discovered that GHRP-1's central dipeptide (Ala-Trp) wasn't essential for GH release. Removing it and making other modifications produced a smaller, cleaner-acting peptide.

The result was Ipamorelin — a five-amino-acid peptide that released growth hormone with potency similar to GHRP-6 but without significant effects on cortisol, prolactin, or aldosterone. The selectivity was remarkable.

In 1998, they published their findings: Ipamorelin was 'the first selective growth hormone secretagogue.' It represented a new generation of GHRPs designed for clinical use.

1999-2008

Clinical Promise

Testing in Humans

Helsinn Therapeutics licensed Ipamorelin and began clinical development. Their target was postoperative ileus — the gut paralysis that often follows abdominal surgery. They hypothesized that GH release might help the gut recover faster.

Phase I trials confirmed Ipamorelin's safety and selectivity in humans. It released growth hormone without the cortisol and prolactin spikes seen with other GHRPs. Patients tolerated it well.

Phase II trials for postoperative ileus, however, were disappointing. The peptide didn't show clear efficacy for that specific indication. Clinical development was discontinued, and Ipamorelin never reached the market.

2008-2018

The Research Peptide Era

Finding New Life Outside Pharma

Though pharmaceutical development ended, Ipamorelin found an audience among researchers and the anti-aging community. Its clean profile made it attractive for those seeking GH benefits without cortisol elevation or appetite stimulation.

Anti-aging clinics began using Ipamorelin, often combined with CJC-1295 (a GHRH analog) for synergistic GH release. The combination became one of the most popular peptide protocols for growth hormone optimization.

The peptide's selectivity also made it useful for research into GH physiology. Scientists could study GH effects without the confounding variables introduced by cortisol and prolactin changes.

2018-Present

The Precision GHRP

Standard for Clean GH Release

Today, Ipamorelin remains the benchmark for selective growth hormone release. When researchers or clinicians want GH stimulation without other hormonal effects, Ipamorelin is typically the choice.

Its profile has been extensively characterized: dose-dependent GH release up to a plateau, minimal desensitization with proper dosing protocols, and consistently clean effects on other hormones. It doesn't cause the intense hunger of GHRP-6 or the cortisol spikes of other GHRPs.

Ipamorelin represents what targeted peptide design can achieve. Though it never reached FDA approval, it demonstrated that GHRPs could be engineered for selectivity — and set the standard for what clean growth hormone stimulation should look like.