If nausea is the reason you’ve hesitated to try a GLP-1, you’re not alone, and the good news is that tolerability varies. Among approved weight loss drugs, tirzepatide (Zepbound, Mounjaro) has shown somewhat fewer treatment-stopping side effects than semaglutide in a head-to-head trial, though both are generally manageable. Most side effects are gastrointestinal (nausea, constipation, diarrhea) and tend to fade as the dose rises slowly. How you start and titrate often matters more than which drug you pick. Here’s the comparison and what actually reduces side effects.<\/p>\n
GLP-1 drugs work partly by slowing stomach emptying, which is also why the most common side effects are digestive: nausea, constipation, diarrhea, and occasional vomiting. These are usually mild to moderate and most pronounced when starting or increasing the dose. For most people they ease over time as the body adjusts.<\/p>\n
Serious side effects are uncommon, and the drugs carry a boxed warning about a rare thyroid tumor risk seen in animal studies. The day-to-day tolerability question, though, is mostly about the stomach.<\/p>\n
The clearest tolerability comparison comes from a direct trial. In the SURMOUNT-5 trial<\/a> published in the New England Journal of Medicine in 2025, tirzepatide and semaglutide were compared head-to-head, and gastrointestinal side effects led to treatment discontinuation less often with tirzepatide (about 2.7%) than with semaglutide (about 5.6%). Both rates are low, which is the more reassuring headline: the large majority of people in both groups stayed on treatment.<\/p>\n