These drugs slow the gut. Food stays in the stomach longer, and the brain reads that fullness as satiety, which is part of how the peptide reduces appetite. Eating too much in one sitting, eating high-fat meals, or eating fast can push that signal into nausea.

In the studies the FDA reviewed before approving Wegovy, about 44% of people on semaglutida had nausea at some point. On placebo, the rate was about 1 in 6. The median episode lasted about 8 days, and cumulative GI events plateaued around week 20 of the dose-up. Tirzepatide showed nausea rates between about 1 in 4 and 1 in 3 across the dose levels, also concentrated in the dose-up phase.