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By HealthVetted Editorial
Reviewed & updated
GLP-1 medications like semaglutide and tirzepatide have changed how many people approach weight management — but they come with side effects worth understanding before you start. Most are gastrointestinal, most are manageable, and most ease as your body adjusts. Here's what the FDA labels actually say, and how to think about each.
This is general information, not medical advice. Every decision about starting, adjusting, or stopping a GLP-1 belongs with a licensed clinician who knows your full history. For a broader overview of how these drugs work, see our [GLP-1 weight loss pillar](/glp-1-weight-loss).
Across the GLP-1 and GLP-1/GIP class, the side effects that show up most often involve the gut. The FDA prescribing information for both Wegovy (semaglutide) and Zepbound (tirzepatide) lists nausea, vomiting, diarrhea, and constipation among the most frequently reported adverse reactions. Abdominal pain, indigestion, and burping are also common.
These effects happen because GLP-1 medications slow gastric emptying — food stays in your stomach longer. That mechanism is part of why they reduce appetite, but it's also why your digestion can feel sluggish or unsettled, especially early on.
| Side effect | Why it happens | General self-management |
|---|---|---|
| Nausea | Slowed stomach emptying | Smaller meals, eat slowly, avoid greasy/rich food |
| Vomiting | Same mechanism, often dose-related | Stay hydrated; contact a clinician if persistent |
| Diarrhea | GI motility changes | Hydrate; replace fluids/electrolytes |
| Constipation | Slowed gut transit | Fluids, fiber, movement |
The table reflects the general categories named in FDA labeling; it is not a dosing or treatment plan. Individual responses vary widely.
A pattern you'll notice across the labels: GI symptoms tend to be most noticeable when you first start and again each time your dose increases. Both the semaglutide and tirzepatide prescribing information build in a stepwise titration schedule precisely for this reason — starting low and increasing gradually gives your body time to adapt and is intended to reduce GI side effects.
This is also true of the diabetes versions of these same molecules. [Ozempic is semaglutide](/reviews/ozempic) approved for type 2 diabetes, and [Mounjaro is tirzepatide](/reviews/mounjaro) approved for type 2 diabetes — same active ingredients, same titration logic, same GI profile.
The practical takeaway: if you feel fine on your current dose and then symptoms return after a dose increase, that timing is expected, not alarming. It usually settles. A clinician may slow your titration or hold a dose if symptoms are hard to tolerate — that's a decision to make together, not on your own. If you want to model what a slower step-down might look like, our [taper calculator](/tools/glp1-taper-calculator) is a planning aid (not medical advice).
The single most important factor in tolerating a GLP-1 is respecting the titration schedule on the label. Going slower than the maximum-speed schedule, when a clinician agrees, is a common way to manage symptoms. The labels for Wegovy and Zepbound both describe escalation over a period of months rather than weeks, and both note that the maintenance dose can be adjusted based on tolerability.
Beyond titration, general comfort measures that align with the slowed-digestion mechanism include eating smaller portions, stopping when full, limiting high-fat and very rich foods, and staying hydrated. None of this is a substitute for clinical guidance, but it follows directly from how the drugs work.
If you're still comparing options, our coverage of [prescription GLP-1s](/best-prescription-glp1) and the [Wegovy vs Zepbound comparison](/compare/wegovy-vs-zepbound) lays out the differences. Some readers also weigh [oral GLP-1 options](/best-oral-glp1) or [compounded versions](/best-compounded-glp1).
Both semaglutide and tirzepatide carry the FDA's most serious warning — a boxed warning — regarding thyroid C-cell tumors. In rodent studies, these drugs caused thyroid C-cell tumors; it is unknown whether they cause such tumors, including medullary thyroid carcinoma (MTC), in humans.
Because of this, the prescribing information directs patients and clinicians to be alert for symptoms that could signal a thyroid tumor, such as a neck mass, trouble swallowing, shortness of breath, or persistent hoarseness. Anyone experiencing these should contact a clinician.
This warning is identical in spirit across Wegovy, Zepbound, and their diabetes counterparts, because the molecules are the same.
The boxed warning translates into a hard contraindication. According to the FDA labels, these medications should not be used by people who have:
If either applies to you, a GLP-1 of this class is not an appropriate option. This is one of the most important screening questions a clinician will ask before prescribing — and one reason self-sourcing these medications without a proper evaluation carries real risk. An [eligibility quiz](/tools/glp1-eligibility-quiz) can help you organize what to discuss, but it does not replace a clinical screening.
Beyond the GI symptoms and the thyroid warning, the FDA labels for these drugs describe additional potential risks that warrant clinical attention, including pancreatitis, gallbladder problems, kidney issues (often linked to dehydration from vomiting or diarrhea), and serious allergic reactions. Labels also note the potential for hypoglycemia, particularly when combined with certain other diabetes medications, and the importance of being aware of any changes in mood.
These are less common than nausea, but they're the reason ongoing clinical follow-up matters. The labels are explicit that severe or persistent symptoms should prompt medical evaluation rather than waiting them out.
Mild, improving nausea or a few days of constipation as your body adjusts is typical. But contact a clinician promptly if you experience:
When in doubt, ask. The cost of an extra phone call is far lower than the cost of ignoring a serious symptom.
For most people, GLP-1 side effects are gastrointestinal, front-loaded, dose-related, and manageable with slow titration and simple eating adjustments. The serious risks — the thyroid boxed warning and the MTC/MEN 2 contraindications — are specific and screenable, which is exactly why these are prescription medications that require a clinician's involvement from start to finish.
If you're evaluating whether a GLP-1 fits your situation, start with the [GLP-1 weight loss overview](/glp-1-weight-loss) and bring your questions to a licensed provider. To compare alternatives, see [supplements vs GLP-1](/supplements-vs-glp1) or [berberine vs Ozempic](/berberine-vs-ozempic).
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For most people, the gastrointestinal side effects are most noticeable when starting and after each dose increase, and tend to ease as the body adjusts. The titration schedules in the FDA labels are designed to reduce these effects by increasing the dose gradually. This is general information, not medical advice — discuss your experience with your clinician.
GLP-1 medications work in part by slowing how quickly your stomach empties, and each dose increase intensifies that effect temporarily. The FDA prescribing information for both semaglutide and tirzepatide builds in stepwise dose increases for this reason. A clinician may slow your titration if symptoms are hard to tolerate.
According to the FDA labels, these medications are contraindicated in people with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2), due to a boxed warning about thyroid C-cell tumors observed in rodent studies. A clinician screens for this before prescribing.
Both semaglutide and tirzepatide carry the FDA's boxed warning because they caused thyroid C-cell tumors in rodents; it is unknown whether they cause such tumors, including medullary thyroid carcinoma, in humans. Patients are advised to watch for symptoms like a neck mass, trouble swallowing, or persistent hoarseness and contact a clinician.
Contact a clinician for severe or persistent vomiting or diarrhea, signs of dehydration, severe abdominal pain that may radiate to the back, a neck lump, hoarseness, trouble swallowing, or signs of a serious allergic reaction. Mild, improving nausea as your body adjusts is more typical, but when in doubt, ask.