Ipamorelin vs GHRP-6 and GHRP-2: What's the Difference?
Ipamorelin, GHRP-6 and GHRP-2 are often searched together by UK researchers, and they are three lab-made peptides from the same family. Researchers call them growth hormone secretagogues, which simply means they all act on the same receptor as ghrelin, a natural peptide made mainly in the stomach. The differences lie in the length of each chain, the amino acids used, and which hormones changed in animal studies.
How Do the Three Peptides Compare?
Ipamorelin is the smallest, with just five amino acids, two of them man-made (Aib and 2-Nal). The same peptide is also supplied as ipamorelin 10mg lyophilised powder. GHRP-6 has six amino acids and was the first peptide of its kind to show strong activity in animals. GHRP-2 also has six and uses the same man-made 2-Nal. All three finish with the same two amino acids, D-Phe and Lys.
According to the 1998 paper that first described ipamorelin, it was found by removing two amino acids (alanine and tryptophan) from the middle of an earlier peptide called GHRP-1.
Which Receptor Do They Act On?
All three act on the growth hormone secretagogue receptor, known as GHSR-1a. Ghrelin was identified as its natural partner in 1999. Ghrelin is a 28-amino-acid peptide, and it only works once a fatty acid group is attached to its third amino acid. A cryo-EM picture of the receptor holding GHRP-6 shows these peptides settling into a split-shaped pocket, as described in a 2025 structural review. Other compounds that act on this receptor family are grouped in our peptides collection.
The original ipamorelin paper only said it worked through a "GHRP-like receptor". Later reviews place it at GHSR-1a because it behaves like the other two, although no dedicated binding study is cited for it.
How Did They Compare in Animal Studies?
In rat pituitary cells, ipamorelin and GHRP-6 released growth hormone at a similar strength. The concentration needed was about 1.3 nM for ipamorelin and 2.2 nM for GHRP-6, and ipamorelin reached about 85% of the largest response GHRP-6 produced.
In pigs, GHRP-2 was the most potent of the three. It took about 0.6 nanomoles per kilogram to get a response, compared with 2.3 for ipamorelin and 3.9 for GHRP-6. GHRP-2 also reached a lower maximum response than the others. Figures like these depend on the exact material tested, which is why batch-level analysis, such as the reports on our lab reports page, matters when results are compared between laboratories.
What Does "Selective" Mean for Ipamorelin?
The word comes from what the researchers measured. In pigs, GHRP-6 and GHRP-2 raised the stress hormones ACTH and cortisol. Ipamorelin did not, even at doses more than 200 times the amount that released growth hormone. None of the three changed FSH, LH, prolactin or TSH. The authors noted that young pigs have few of the cells that make prolactin alongside growth hormone, which may explain why prolactin stayed flat.
So "selective" describes the hormones that were measured in that animal and age group.
Important: This article is for scientific information only. The peptides discussed are intended exclusively for scientific and laboratory research and are not intended for human or veterinary consumption, administration, diagnosis, treatment or therapeutic use.