Ipamorelin side effects: what was measured, not what is rumoured

What "side effects" can mean for an unapproved peptide

An approved drug has a label with an adverse-event table built from thousands of patients. Ipamorelin has three human studies, none of which had growth hormone as its purpose, and a body of animal pharmacology from the company that designed it. So the honest answer to "what are the side effects of ipamorelin" has four parts: what its designers measured in animals, what the human studies recorded, what the class it belongs to is known to do, and what has never been looked at. This page keeps the four apart.

Cortisol, prolactin and the rest: the selectivity data

Ipamorelin was made to avoid the main off-target effect of earlier GHRPs. Raun and colleagues measured it directly in conscious swine. GHRP-6 and GHRP-2 raised plasma ACTH and cortisol along with GH. Ipamorelin did not: its ACTH and cortisol responses were not significantly different from those after GHRH, the reference secretagogue that acts only on the GHRH receptor, and that held at doses more than 200-fold higher than the ED50 for GH release (2.3 nmol/kg). None of the secretagogues tested changed FSH, LH, prolactin or TSH [Raun et al., 1998].

Those are the numbers behind the claim, repeated on many pages, that ipamorelin "does not raise cortisol". The claim is true as far as it goes; what it omits is that it rests on swine and on a single study from the manufacturer, and that no human trial has ever measured cortisol or prolactin after ipamorelin. The comparison point is informative: GHRP-6 in normal men raised prolactin and cortisol about 2-fold at 1 µg/kg [Bowers et al., 1990]. The whole point of ipamorelin's design was to lose that, and the animal data say it did.

What the human studies recorded

Swipe sideways to see the whole table.

The 2014 trial is the only controlled human safety dataset of any size, and it should be read for what it is: hospital inpatients recovering from bowel surgery, in whom an adverse-event rate near 90 % in both arms reflects the surgery, not the drug. The finding that matters is the comparison, 87.5 % against 94.8 %, and the investigators' conclusion that the regimen was well tolerated [Beck et al., 2014]. The 320-patient successor would have been the dataset that itemised events by dose; it was completed and never published [Helsinn et al., 2011], which is itself a fact worth weighing. Nothing in those trials speaks to weeks or months of subcutaneous use, because none was studied.

Desensitisation: one signal, in rats

A receptor stimulated repeatedly can respond less. The one published test of this for ipamorelin is in the 1999 rat bone study. After 15 days of subcutaneous dosing three times daily, the animals' GH response to a provocative intravenous dose of ipamorelin was marginally reduced (P < 0.03), while the response to GHRH was unchanged and the pituitary GH content was normal [Johansen et al., 1999].

The reading is that the ghrelin receptor had become slightly less responsive, the GHRH receptor had not, and the gland had not emptied. Whether the same happens in people, at what dose and after how long, has not been measured. Any statement about "tolerance" to ipamorelin in humans is inference from that one rat paragraph.

Effects shared by the GHRP class

Ipamorelin belongs to the family of ghrelin-receptor agonists, and ghrelin is the hormone of hunger. Ghrelin-receptor stimulation promotes gastric motility, which is exactly why Helsinn tested ipamorelin in postoperative ileus [Beck et al., 2014]. Increased appetite is therefore a mechanism-based expectation for any molecule in the class, even though no ipamorelin study reports it as an outcome. Water retention, tingling and glucose changes are described in the literature on growth hormone itself and are plausible downstream of any secretagogue; they have not been measured for ipamorelin. The CJC-1295 side effects page covers the GHRH half of the pair, where flushing and injection-site reactions are documented.

The FDA's 2023 sentence

The most consequential recent statement about ipamorelin's safety is regulatory, not clinical. On September 29, 2023 the FDA placed ipamorelin acetate in category 2 of the bulk drug substances nominated for compounding under sections 503A and 503B of the Food, Drug and Cosmetic Act: the category for substances that "may present significant safety risks".

The agency's stated reason is that compounded drugs containing ipamorelin acetate may pose a risk for immunogenicity for certain routes of administration [U.S., 2023]. In practice, that removed the compounding route through which most US clinics had been dispensing it. Ipamorelin is also listed by name under growth hormone secretagogues in class S2 of the WADA Prohibited List, prohibited at all times [World, 2026].

What has not been measured

• No human study has measured cortisol, prolactin, glucose, insulin or IGF-1 after ipamorelin.
• No human study has used the subcutaneous route or exposures longer than 7 days.
• No human study has given ipamorelin together with CJC-1295 or any GHRH analogue.
• The immunogenicity concern the FDA cited has not been quantified in a published study.

A page that fills those gaps with confident sentences is not reporting; it is guessing. The doses used in the studies above are collected in the dosage guide.

Questions or corrections: editor@cjc-1295-ipamorelin.com. See the editorial policy.