Ipamorelin vs GHRP-2: what to choose and for whom

Ipamorelin is often marketed as the “mildest” peptide for stimulating growth hormone, and GHRP-2 as “more potent, but with side effects”. This description partly relies on real studies but draws the wrong conclusions from them. The editorial team explains how to approach the question “what to choose” soberly and why, for most people, both answers are wrong.

Where the idea of a “mild” and a “strong” peptide came from

Ipamorelin’s reputation as a “mild” peptide comes from the preclinical study by Raun and colleagues (1998): in animals it stimulated GH release without substantially raising ACTH and cortisol, whereas GHRP-6 and GHRP-2 did have such an effect. This result is indeed important for pharmacology, but it concerns laboratory animals and certain doses.

GHRP-2’s reputation as “strong” is related to it being one of the most potent GH stimulators in its class. That is precisely why in Japan pralmorelin is used as a diagnostic agent: a single administration allows an assessment of whether the pituitary is able to release growth hormone.

However, in everyday logic “mild” quickly turns into “safe”, and “strong” into “more effective for muscle”. Both transformations are incorrect. Selectivity with respect to cortisol does not remove the risks associated with growth hormone itself and IGF-1, and the potency of GH release in a diagnostic test does not mean a benefit for body composition.

For healthy people and athletes there are no studies in the peer-reviewed literature that would show that any of these peptides improves strength, muscle mass or recovery.

How to think about the choice

A rational choice of any intervention consists of three questions: is there a problem that needs solving; is it proven that the agent solves it; and is the price in the form of risks acceptable. For unregistered peptides in a healthy person the chain breaks already at the second step.

If, however, the problem is medical — for example, a suspected growth-hormone deficiency — the decision is made by an endocrinologist, and their arsenal includes registered diagnostic tests and recombinant growth hormone with a known safety profile. Peptides from “research” sites do not fit into this scheme.

That is why the editorial team suggests replacing the question “ipamorelin or GHRP-2” with the question “why am I considering intervention in the hormonal system, and have I exhausted the safe ways to reach my goal”.

Below we nevertheless compare the peptides by risk criteria — not as a recommendation, but to show that even the “mildest” option is not neutral.

For whom these peptides are especially risky

For some people even the hypothetical use of secretagogue peptides is associated with disproportionately high risks. Some of them concern both substances, some primarily GHRP-2.

• People with cancers or a history of cancer— a rise in IGF-1 as a cell growth factor.
• People with diabetes or insulin resistance— the effect of GH and cortisol on glucose metabolism.
• People with pituitary diseases, in particular a prolactinoma— especially with regard to GHRP-2.
• Children and adolescents— interference with growth processes.
• Pregnant and breastfeeding women.
• Athletes subject to testing— both peptides are directly named in class S2 of the WADA list.

People with sleep disorders, high stress levels or a tendency to edema should also remember that an effect on cortisol and water-salt balance may worsen their well-being.

Separately about older people: interest in peptides is often fueled by promises of “rejuvenation”. However, it is precisely in older people that the side effects of stimulating the GH axis — edema, joint pain, worsened glucose tolerance — appear most often.

For everyone else the argument is the same: the absence of evidence of benefit and of long-term safety data.

The problem of product quality

Even if the pharmacology of the peptide were ideal, the buyer of an illegal product faces another problem: they do not know exactly what is in the vial. Analyses of “research peptide” products carried out by anti-doping laboratories have repeatedly found discrepancies with the declared composition, impurities and breakdown products.

Lyophilized peptides are sensitive to temperature, moisture and light. Violations of storage and transport conditions can lead to degradation of the peptide, aggregation and the formation of by-products. Pharmaceutical manufacturers control these parameters, whereas on the “gray” market they do not.

Another risk is sterility. Products made outside good manufacturing practice (GMP) conditions may contain bacterial endotoxins, which cause fever, inflammation at the injection site and systemic reactions.

Finally, the label “not for human consumption” means that the manufacturer bears no responsibility for the consequences. For the consumer this is a signal, not a formality.

Evidence-based alternatives

Natural growth-hormone secretion is best supported by sleep, physical activity and a normal body weight. A significant part of the daily GH release falls during deep sleep, so a sleep schedule and treatment of apnea give a physiological effect without intervention in the endocrine system.

For increasing muscle mass and strength, progressive strength training, protein at the level of 1.4–2.0 g/kg of body weight per day per the ISSN position and creatine monohydrate have an evidence base. For recovery, periodization of loads, nutrition and sleep are important.

If, however, there are symptoms that may indicate hormonal disorders — persistent fatigue, loss of muscle mass, changes in body composition without visible causes — it is worth seeing an endocrinologist. GH deficiency is diagnosed according to clinical guidelines, and treated with registered agents.

Such a path is less “fast”, but it answers the question of whether there is a problem at all, and does not create new ones.

Editorial conclusions

Ipamorelin differs from GHRP-2 in a smaller effect on cortisol and prolactin in preclinical studies, and GHRP-2 in greater potency of GH stimulation and a narrow diagnostic use. But neither peptide has a proven benefit or long-term safety data for healthy people, both are banned by WADA, and the quality of products on the market is not guaranteed.

That is why the editorial team does not consider either of them a rational choice outside a medical context. For people with cancer risks, diabetes, pituitary diseases, for athletes, children and pregnant women, these peptides are especially contraindicated.

We also recommend reading “Ipamorelin or GHRP-2: what is the difference”, our material on quality control and storage of peptides and an article on sleep as a natural regulator of growth hormone.

References

1. Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol. 1998;139(5):552–561.
2. Bowers CY. Growth hormone-releasing peptide (GHRP). Cell Mol Life Sci. 1998;54(12):1316–1329.
3. Sigalos JT, Pastuszak AW. The safety and efficacy of growth hormone secretagogues. Sex Med Rev. 2018;6(1):45–53.
4. Molitch ME, Clemmons DR, Malozowski S, et al. Evaluation and treatment of adult growth hormone deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(6):1587–1609.
5. Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20.
6. World Anti-Doping Agency. The World Anti-Doping Code International Standard: Prohibited List. Montreal: WADA; чинна редакція.