GLP-1 side effects: what's common and why
Key takeaways
- The most common side effects are digestive — nausea, vomiting, diarrhea, and constipation.1,2
- They happen because these medicines slow how fast your stomach empties.1
- They’re generally most noticeable when you start or increase a dose.3
- Rarer serious risks exist (pancreatitis, gallbladder, kidney, low blood sugar, a thyroid-tumor warning) — ones the FDA and NIH say to know about and raise with your doctor.1,3
GLP‑1 medications — semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) — are well known for digestive side effects. Here’s what the FDA prescribing information and the NIH actually say, in plain language.
What are the most common side effects?
The NIH’s MedlinePlus drug pages list the most common side effects of semaglutide as nausea, vomiting, diarrhea, stomach pain, and constipation,1 and for tirzepatide as nausea, vomiting, diarrhea, decreased appetite, constipation, and upset stomach.2 In other words: the usual ones are digestive.
Why do they cause stomach trouble?
According to MedlinePlus, semaglutide “slows the emptying of the stomach and may decrease appetite.”1 That slowed-down stomach is part of how these medicines help you feel full — and also why the side effects people notice most are things like nausea, fullness, and constipation.
Do they get better over time?
These effects are generally most noticeable when you start the medication or move up to a higher dose.3 MedlinePlus advises telling your doctor if any of them are severe or don’t go away.1 Everyone’s different, so what your own experience looks like is a good thing to track and bring to your next appointment.
What about serious side effects?
Less commonly, the prescribing information lists serious risks to be aware of — including pancreatitis, gallbladder problems, kidney problems, low blood sugar (especially alongside insulin or certain other diabetes medicines), and allergic reactions.1 The label also carries a boxed warning about thyroid C‑cell tumors seen in rodents, and says semaglutide should not be used by people with a personal or family history of medullary thyroid carcinoma or MEN 2.3
These are things to understand and discuss with your clinician — not to self-diagnose. If you’re weighing what any of this means for you, that’s exactly the conversation to have with the person who prescribed your medication.
Frequently asked
What is the most common side effect of GLP-1 medications?
Nausea. The NIH's MedlinePlus pages list nausea, vomiting, and diarrhea among the most common side effects of both semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound).
Why do these medications cause stomach side effects?
They slow how fast your stomach empties, which is part of how they curb appetite — and also why the most common side effects are digestive ones like nausea and constipation, according to MedlinePlus.
Are GLP-1 side effects dangerous?
Most reported side effects are digestive. The prescribing information also lists rarer but serious risks — including pancreatitis, gallbladder problems, kidney problems, low blood sugar, and a thyroid-tumor warning — that the FDA and NIH say to be aware of and discuss with your doctor. This is general information, not medical advice.
Sources
- Semaglutide Injection — MedlinePlus Drug Information — U.S. National Library of Medicine (NIH)
- Tirzepatide Injection — MedlinePlus Drug Information — U.S. National Library of Medicine (NIH)
- Ozempic (semaglutide) Prescribing Information — DailyMed — U.S. FDA / NIH DailyMed