Types of peptides

What are the main classes of peptides?

FDA defines a peptide as an amino-acid chain of 40 or fewer amino acids [1]. Within that definition, GLP-1 receptor agonists such as semaglutide, sold as Wegovy, are approved "to reduce excess body weight and maintain weight reduction long term" in adults and pediatric patients aged 12 and older with obesity [2], and GHRH analogs include tesamorelin, approved in 2010 for HIV-associated lipodystrophy [3]. GH secretagogues such as ipamorelin, growth hormone fragments such as AOD-9604, copper peptides such as injectable GHK-Cu and mitochondrial-derived peptides such as MOTS-c are studied compounds whose nominations FDA's Category 2 page records as withdrawn; ipamorelin acetate also stays active in 503B Category 2 [4].

Which classes include FDA-approved drugs, and which don't?

Melanocortin peptides include PT-141 and melanotan II; FDA's Category 2 page records melanotan II's nomination as withdrawn and cites published case reports of "melanoma, posterior reversible encephalopathy syndrome, sympathomimetic toxidrome and priapism" [4]. Tissue-repair peptides like BPC-157 and TB-500, injectable GHK-Cu, and neuropeptides like Semax and Selank all carry withdrawn 503A nominations rather than approval [4].

Does a peptide's class decide whether it can be compounded?

No. Each substance is evaluated on its own, and FDA's Category 2 page shows the range within one class: among growth hormone secretagogues, ipamorelin acetate is an active 503B Category 2 listing, GHRP-2 and GHRP-6 are 503B Category 2 entries dated September 29, 2023, and ibutamoren mesylate sits in both 503A and 503B Category 2 after a trial "was terminated early due to a potential safety signal of congestive heart failure" [4].