About 1 in 8 American adults say they take a drug like Ozempic or Zepbound. The first GLP-1 drug, Byetta, was a synthetic copy of a peptide from Gila monster venom. Human GLP-1, the gut hormone that tells the pancreas to release insulin, lasts about 2 minutes in the body. An enzyme called DPP-4 cuts off its first two amino acids, right after the alanine in position 2, and the shortened hormone no longer triggers insulin release. The lizard's peptide has glycine there, and DPP-4 doesn't cut glycine. Its synthetic copy, exenatide, lasts 2.4 hours. John Eng, an endocrinologist at a veterans' hospital in the Bronx, read that Gila monster venom made the pancreas swell. In 1992 he pulled a 39-amino-acid peptide out of that venom. About half its amino acids matched human GLP-1. Eng's employer, the VA, declined to patent it because it wasn't specific to veterans, so he filed the patent himself in 1993. For 3 years, almost every big diabetes drugmaker ignored him or passed. In 1996 Amylin licensed it, and the FDA approved it as Byetta in 2005. Novo Nordisk built Ozempic from human GLP-1, so DPP-4 would cut it too. Ozempic's semaglutide swaps that second alanine for Aib, an amino acid that isn't in human proteins, to protect it from DPP-4. Eli Lilly partnered with Amylin on Byetta from 2002 to 2011. In 2025, Lilly's own GLP-1 drug, tirzepatide (Zepbound and Mounjaro), sold $36.5B and passed Merck's Keytruda as the world's best-selling drug. Lilly ended tirzepatide's chain with amino acids copied from the monster's peptide.