There is a medical condition called gastroparesis: severe, chronic delayed stomach emptying, usually diagnosed in people with long-standing diabetes or after certain abdominal surgeries. The peptide does not cause that condition. What the peptide does is slow stomach emptying as part of the mechanism that reduces appetite.

In the pooled studies behind the Wegovy approval, severe GI side effects (the most extreme cases of nausea, vomiting, and stomach discomfort) showed up in about 1 in 25 people on the peptide, compared with about 1 in 100 on placebo. A specific substudy in STEP-1 measured stomach emptying at 20 weeks using a paracetamol-absorption test and did not find a residual delay at that point. The Wegovy label does caution against use in patients with severe gastroparesis at the start of treatment.