Why are some peptides FDA-approved drugs and others only "research" chemicals?

The split is about trials and paperwork, not chemistry. To become an approved drug, a peptide goes through Phase 1 to 3 human trials, then a New Drug Application or Biologics License Application the FDA reviews for safety and effectiveness for a specific use. Insulin, semaglutide, tirzepatide, and tesamorelin all cleared that path. Many others never did. Per a Pharmacy Times review, BPC-157 has over 100 animal studies but only a handful of small human trials, none meeting the bar for approval. So it has no approved indication. A lot of it is economics. Peptides that can't be patented give companies little reason to fund a full approval, which industry write-ups put near $1 to 2 billion. Without it, vendors label them "research use only," a category for lab work, not a green light to take them. Use questions go to a licensed provider.