Quick answer: The most common side effects listed for FDA-approved GLP-1 medicines such as Wegovy and Zepbound are gastrointestinal: nausea, diarrhea, vomiting, constipation, and stomach pain. In the STEP 1 and SURMOUNT-1 trials, most GI events were mild to moderate. FDA labels also carry serious warnings, so any GLP-1 decision belongs with a licensed clinician.
Why people search "GLP-1 side effects" first
Before anyone asks whether a GLP-1 medicine might fit them, they usually ask a simpler question: what does it feel like, and what can go wrong? That is a reasonable place to start. This guide sticks to what the U.S. Food and Drug Administration (FDA), the National Library of Medicine, and peer-reviewed trials actually report. It does not predict how any one person will respond.
A quick vocabulary note. "GLP-1" is shorthand for glucagon-like peptide-1 receptor agonists such as semaglutide (sold as Ozempic and Wegovy). Tirzepatide (sold as Mounjaro and Zepbound) acts on both GLP-1 and GIP receptors, according to FDA. People often group them together, so we cover both here.
What FDA lists as the most common side effects
Semaglutide (Wegovy)
In its March 2024 announcement of a cardiovascular indication for Wegovy, FDA listed the most common side effects as nausea, diarrhea, vomiting, constipation, abdominal (stomach) pain, headache, fatigue, dyspepsia (indigestion), dizziness, abdominal distension, belching, low blood sugar in patients with diabetes, flatulence, and gastroesophageal reflux disease (heartburn).
Tirzepatide (Zepbound)
In its December 2024 announcement for obstructive sleep apnea, FDA listed Zepbound side effects including nausea, diarrhea, vomiting, constipation, abdominal discomfort and pain, injection site reactions, fatigue, hypersensitivity (allergic) reactions, burping, hair loss, and gastroesophageal reflux disease.
The patient-facing version
MedlinePlus, the National Library of Medicine's consumer drug resource, lists nausea, vomiting, diarrhea, stomach pain, constipation, heartburn, burping, runny nose or sore throat, and headache as semaglutide side effects to report if they are severe or do not go away. For tirzepatide, it lists nausea, vomiting, diarrhea, decreased appetite, constipation, and upset stomach.
What the large trials reported
Labels tell you what can happen. Trials give a sense of how it showed up in specific study groups.
- STEP 1 (semaglutide, NEJM 2021). Nausea and diarrhea were the most common adverse events. The authors described them as typically transient, mild to moderate, and subsiding with time. More participants stopped treatment because of GI events on semaglutide (4.5%) than on placebo (0.8%).
- SURMOUNT-1 (tirzepatide, NEJM 2022). The most common adverse events were gastrointestinal, mostly mild to moderate, and occurred mainly during dose escalation. Adverse events led to discontinuation in 4.3% to 7.1% of tirzepatide groups versus 2.6% on placebo.
These are group results from trial populations with close follow-up. They are not a forecast for you, and real-world experience can differ.
Serious warnings on the labels
Common side effects are only half the picture. FDA's Wegovy announcement describes a boxed warning about thyroid C-cell tumors and says Wegovy should not be used by people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). FDA's Zepbound announcement notes that tirzepatide causes thyroid C-cell tumors in rats and that it is unknown whether it causes such tumors in humans.
FDA also lists warnings for Wegovy that include:
- Inflammation of the pancreas (pancreatitis)
- Gallbladder problems, including gallstones
- Low blood sugar, especially when combined with insulin or drugs that raise insulin
- Acute kidney injury
- Hypersensitivity (allergic) reactions
- Diabetic retinopathy
- Increased heart rate
- Suicidal behavior or thinking
Symptoms MedlinePlus says need prompt attention
MedlinePlus tells semaglutide users to call a doctor right away, or get emergency care, for ongoing pain that starts in the upper left or middle of the stomach and may spread to the back; rash, itching, or swelling of the face, mouth, or throat; fainting or dizziness; trouble breathing or swallowing; or decreased urination or swelling of the legs. If you are on any medicine and something feels seriously wrong, contact a clinician or emergency services. Don't wait for a blog post.
Compounded and "research" products are a different conversation
Everything above comes from studies of FDA-approved brand products. FDA states that compounded drugs are not FDA-approved and are not reviewed for safety, effectiveness, or quality before they are marketed. FDA has also warned about products sold "for research purposes" or "not for human consumption" that contain semaglutide, tirzepatide, or retatrutide. Retatrutide is investigational. FDA says it cannot be used in compounding under federal law and has not been found safe and effective for any condition.
That matters for side effects. Label data and trial data describe the approved product studied. They do not automatically transfer to a product with a different source, strength, or ingredients. Our 503A vs 503B explainer covers sourcing in more depth.
How a physician-led visit approaches side effects
We won't give dosing, titration, or "how to manage nausea" protocols here. Those are individual medical decisions. In general, a responsible GLP-1 conversation with a licensed clinician covers:
- Your history. Thyroid cancer or MEN 2 in you or your family, pancreatitis, gallbladder disease, kidney problems, diabetic eye disease, depression, pregnancy plans.
- Your other medicines. Especially insulin or other drugs that lower blood sugar.
- What product is actually being discussed. FDA-approved brand, compounded, or something else.
- Follow-up. Who you contact if side effects happen, and how quickly.
Frequently asked questions
What is the most common side effect of GLP-1 medicines?
Gastrointestinal effects are the most commonly reported. FDA lists nausea, diarrhea, vomiting, constipation, and abdominal pain among the most common side effects of Wegovy and Zepbound. In STEP 1, nausea and diarrhea led the list for semaglutide. How often and how strongly they occur varies from person to person.
Do GLP-1 side effects go away?
In STEP 1, investigators reported that nausea and diarrhea were typically transient and mild to moderate, and they subsided over time. In SURMOUNT-1, GI events happened mostly during dose escalation. Those are trial-group observations, not a promise. Tell your clinician about any symptom that lasts or gets worse.
Is hair loss a side effect of Zepbound?
FDA's December 2024 Zepbound announcement lists hair loss among the side effects of Zepbound, along with nausea, diarrhea, vomiting, constipation, and others. If you notice hair changes on any medicine, bring it up with the prescribing clinician. Many different factors can affect hair.
Who should not take Wegovy?
FDA says Wegovy should not be used by people with a personal or family history of medullary thyroid carcinoma or MEN 2, or by people with a history of severe allergic reaction to semaglutide or its ingredients. Only a licensed clinician who reviews your full history can decide what fits you.
Do compounded GLP-1s have the same side effects as brand drugs?
No one can assume so. FDA says compounded drugs are not FDA-approved and aren't reviewed for safety, effectiveness, or quality before marketing. Label and trial safety data describe the approved products that were studied.
Talk with a Regen Therapy MD physician
If you'd like to talk through whether any of these options fit your health history, start with a physician consult, not a product.
- Book a consult: https://book.mypatientnow.com/practice/TqZLiT
- Call: (424) 349-6008
- Cost: $295 consult (physician visit)
- Clinics: Beverly Hills and Santa Monica. Telehealth and peptide shipping are available only where we are licensed.
Sources
- U.S. FDA. FDA Approves First Treatment to Reduce Risk of Serious Heart Problems Specifically in Adults with Obesity or Overweight (Wegovy), March 8, 2024. https://www.fda.gov/news-events/press-announcements/fda-approves-first-treatment-reduce-risk-serious-heart-problems-specifically-adults-obesity-or
- U.S. FDA. FDA Approves First Medication for Obstructive Sleep Apnea (Zepbound), December 20, 2024. https://www.fda.gov/news-events/press-announcements/fda-approves-first-medication-obstructive-sleep-apnea
- MedlinePlus (NIH/NLM). Semaglutide Injection. https://medlineplus.gov/druginfo/meds/a618008.html
- MedlinePlus (NIH/NLM). Tirzepatide Injection. https://medlineplus.gov/druginfo/meds/a622044.html
- Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021. PMID 33567185. https://pubmed.ncbi.nlm.nih.gov/33567185/
- Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022. PMID 35658024. https://pubmed.ncbi.nlm.nih.gov/35658024/
- U.S. FDA. FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss. https://www.fda.gov/drugs/drug-alerts-and-statements/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss
Educational disclaimer
This article is for educational purposes only and is not medical advice, diagnosis, or treatment. It doesn't establish a doctor-patient relationship or confirm that you are a candidate for any therapy. Individual results vary, and no outcome is promised. Study figures are group results from the cited publications, not predictions for any individual. Compounded drugs are not FDA-approved, and FDA-approved brand products and compounded preparations are not interchangeable. Retatrutide is investigational. This article doesn't provide dosing or treatment protocols. Talk with a licensed clinician about your own situation. If you have a medical emergency, call 911.
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