The second hormone that made the newest drugs hit harder.

If GLP-1 is the famous incretin, GIP is the quiet one that explains why tirzepatide outperformed the drugs before it.

GIP stands for glucose-dependent insulinotropic polypeptide. Like GLP-1, it is an incretin released by the gut after eating, and like GLP-1 it stimulates insulin only when glucose is high. For decades it was considered the lesser of the pair. That changed when tirzepatide combined GIP activity with GLP-1 activity in one molecule. In head-to-head trials, the combination produced larger weight loss than GLP-1 alone, with reported results climbing past twenty percent of body weight at the higher doses.

Now the honest part the marketing skips. Researchers do not fully agree on why adding GIP helps. In some studies activating GIP improves outcomes. In others, blocking GIP appears to help as well. Both an agonist and an antagonist have shown benefit in different contexts. This is an open scientific question, not a settled one, and anyone who explains GIP with total confidence is selling rather than teaching.

What you can take away is concrete. GIP is the second lever. Tirzepatide pulls it alongside GLP-1, and that combination is why it sits a tier above single-hormone drugs in reported results.