Common Side Effects of GLP-1 Medications: Mounjaro & Wegovy Explained

The Most Common Side Effects: Gastrointestinal Dominance

Gastrointestinal side effects are by far the most prevalent, affecting approximately 50-60% of patients during initial treatment phases. However, these effects are typically dose-dependent and diminish significantly over time.​

Nausea and Vomiting

Nausea is the #1 reported side effect, occurring in approximately 21.5% of GLP-1 users. Vomiting affects roughly 9% of patients. These symptoms are worst during dose escalation and generally improve after 2-4 weeks. Semaglutide (Wegovy) users report slightly lower nausea rates (~20%) compared to tirzepatide (Mounjaro) users.​

Diarrhea and Constipation

Conflicting gastrointestinal effects occur frequently:

• Diarrhea: Affects 10.6% of users​
  
  
• Constipation: Affects 7.9% of users​
  
  

Interestingly, patients may experience both alternately rather than consistently one or the other.​

Other Common GI Symptoms

• Stomach pain/discomfort: Up to 8% incidence​
  
  
• Bloating and gas: Frequently reported, particularly with Mounjaro​
  
  
• Heartburn/acid reflux: Occurs in roughly 1 in 10 users​
  
  
• Loss of appetite: Affects 5.5% of patients​
  
  

Tirzepatide (Mounjaro) vs. Semaglutide (Wegovy): Side Effect Differences

Critical finding: Tirzepatide users experience significantly more gastrointestinal side effects than semaglutide users:​

• Tirzepatide: 79.8% experience GI adverse events​
  
  
• Semaglutide: 30.8% experience GI adverse events​
  
  

However, semaglutide carries higher risks for pancreatitis (2.62× higher), thyroid malignancy (4.32× higher), and elevated blood sugar.​

Secondary and Systemic Side Effects

Fatigue and Dizziness: Common during initial treatment, often resolving as your body adapts​

Hair Loss: Reported by some users, likely due to rapid weight loss and nutrient deficiencies rather than direct medication effect​

Headaches: Often secondary to dehydration from vomiting and diarrhea​

Injection Site Reactions: Mild redness, swelling, or bruising at injection sites (less common with modern formulations)​

Rare But Serious Side Effects

Pancreatitis: Inflammation of the pancreas presenting with severe abdominal pain radiating to the back, nausea, fever, and vomiting. Seek emergency care immediately.​

Gallbladder Issues: Including gallstones and acute cholecystitis (inflammation), occurring in approximately 1-2% of users​

Kidney Injury: Tirzepatide associated with higher acute kidney injury risk​

Anaphylaxis: Extremely rare severe allergic reaction requiring immediate 999 call​

Management Strategies

For nausea: Eat small, frequent meals; avoid high-fat foods; stay hydrated; sip ginger or peppermint tea​

For constipation: Increase fiber intake, hydration, and physical activity​

Dose adjustment: Most side effects resolve by lowering dose or slowing titration schedulestandfonline​

Bottom Line

GLP-1 side effects are predominantly gastrointestinal and temporary. Mounjaro causes more GI issues than Wegovy, but Wegovy carries higher serious adverse event risk. Most patients tolerate treatment well after 4 weeks as symptoms naturally diminish. Always discuss side effect management strategies with your healthcare provider—medication modifications exist to optimize your treatment experience.​

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC12270588/
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC12491879/
3. https://www.goodrx.com/classes/glp-1-agonists/glp-1-side-effects
4. https://www.emjreviews.com/gastroenterology/news/weighing-up-the-risks-gi-side-effects-of-semaglutide-vs-tirzepatide/
5. https://www.goodrx.com/ozempic/semaglutide-side-effects
6. https://www.numan.com/weight-loss/medication/wegovy-side-effects
7. https://onlinedoctor.boots.com/weight-loss/wegovy-saxenda-side-effects
8. https://www.ahajournals.org/doi/10.1161/circ.150.suppl_1.4142273
9. https://www.tandfonline.com/doi/abs/10.1080/17474124.2025.2579117
10. https://pmc.ncbi.nlm.nih.gov/articles/PMC10960895/

‍