FDA labels list hair loss in 3% of Wegovy and 4–5% of Zepbound users, but the real trigger is rapid weight loss producing telogen effluvium — a reversible 6–12 month shedding pattern. This guide covers the FDA evidence, the timeline you can plan around, why women report it more often, the genetic variants behind GLP-1 response, and how a slower-titration PlexusDx protocol plus the Precision Peptide Genetic Test reduces risk before week one.