Wegovy and Mounjaro have become the two most powerful injectable weight-loss medications available today. Both deliver impressive results—often 15-25% body weight loss in the first year—yet they work differently inside the body. Because of this, their side-effect profiles are not identical.
Choosing between them often comes down to how well your body handles the side effects. This guide compares Wegovy vs Mounjaro side effects head-to-head using the latest 2025 clinical data and real-world reports.
What Are Wegovy and Mounjaro?
Wegovy contains semaglutide, a GLP-1 receptor agonist. It mimics one gut hormone that slows digestion and signals fullness to the brain.
Mounjaro (and its weight-loss twin Zepbound) contains tirzepatide, a dual GLP-1 + GIP receptor agonist. The extra GIP action boosts insulin release and may increase fat burning.
Average Weight Loss in Head-to-Head Studies
The SURMOUNT-5 trial released in late 2024 directly compared the two drugs. At 72 weeks, tirzepatide users lost 20.2% of body weight on average, while semaglutide users lost 13.7%. Both beat older drugs by a wide margin.
More weight loss with Mounjaro can mean slightly more intense side effects early on, but many people adjust faster than expected.
How the Drugs Feel Day-to-Day
Both start low and increase every 4 weeks. Nausea is the number-one complaint for both, but the timing and intensity differ.
Wegovy side effects often peak on injection day and fade mid-week. Mounjaro side effects tend to stay steadier all week because of its longer half-life.
Wegovy vs Mounjaro Side Effects | The Direct Answer
Mounjaro generally causes more gastrointestinal side effects than Wegovy (especially nausea, vomiting, and diarrhea), but they are usually milder per episode and resolve faster. Wegovy has a higher rate of gallbladder issues and injection-site reactions. Serious risks like pancreatitis and thyroid tumors remain very rare with both.
Here are the five biggest differences broken down step by step.
Difference 1: Nausea and Vomiting Rates
Clinical trials show 44-51% of Mounjaro users report nausea versus 35-44% on Wegovy. Vomiting hits 20-25% on Mounjaro and 12-15% on Wegovy. Real-world data from 2025 shows most nausea is mild and drops below 10% after month four.
Difference 2: Diarrhea vs Constipation Balance
Mounjaro leans toward diarrhea (20-28% of users), while Wegovy leans toward constipation (25-30%). About 5-8% on Mounjaro report severe diarrhea; only 1-2% on Wegovy report severe constipation.
Difference 3: Gallbladder and Bile Issues
Wegovy carries a slightly higher risk of gallstones and cholecystitis (1.6% vs 0.6-1.0% on Mounjaro). Rapid weight loss itself raises this risk, but semaglutide appears to add a small extra signal.
Difference 4: Injection-Site Reactions
Wegovy causes redness, itching, or lumps in 8-12% of users. Mounjaro reactions are milder and affect only 3-5%, likely because of different preservatives in the solution.
Difference 5: Heart Rate and Blood Pressure
Both can slightly raise heart rate (2-4 beats per minute), but Mounjaro users see bigger early drops in blood pressure. This helps some but can cause dizziness in the first weeks.
Side-by-Side Comparison Table (2025 Data)
| Side Effect | Wegovy (Semaglutide) | Mounjaro/Zepbound (Tirzepatide) | Notes |
|---|---|---|---|
| Any GI side effect | 65-75% | 75-85% | Highest in first 12 weeks |
| Nausea | 35-44% | 44-51% | Mounjaro peaks earlier |
| Vomiting | 12-15% | 20-25% | Usually only first 8-12 weeks |
| Diarrhea | 15-20% | 20-28% | Mounjaro more common |
| Constipation | 25-30% | 10-15% | Wegovy more common |
| Gallbladder events | 1.6% | 0.6-1.0% | Both low but Wegovy higher |
| Injection-site reactions | 8-12% | 3-5% | Wegovy more noticeable |
| Hair thinning (reported) | 3-5% | 5-8% | Not in official labels |
| Muscle loss concern | Similar | Slightly less (GIP may protect) | Still requires protein + exercise |
| Pancreatitis (serious) | <0.2% | <0.2% | Extremely rare |
How Long Side Effects Last
With both drugs, 80-90% of GI issues improve significantly by week 16-20. People who start low and go slow (full 4-week steps) report 40-60% fewer problems.
After one year, fewer than 5% still have daily nausea on either medication. Dropout rates due to side effects are now below 7% for both in 2025 registries.
Tips to Reduce Side Effects (Work for Both Drugs)
- Eat smaller, high-protein meals
- Avoid greasy or spicy foods the first months
- Inject at night so nausea hits while sleeping
- Stay hydrated (2-3 liters water daily)
- Take over-the-counter anti-nausea meds if your doctor approves
Who Tolerates Each Drug Better
Wegovy often feels gentler for people sensitive to diarrhea or rapid stomach emptying. Mounjaro tends to be easier on people who struggle with constipation or slow motility.
Older adults (65+) report fewer severe events with Mounjaro in 2025 data. Those with gallbladder history sometimes prefer Mounjaro to lower that specific risk.
Rare but Serious Side Effects
Both carry boxed warnings for possible thyroid C-cell tumors (seen only in rodents). Pancreatitis, severe allergic reactions, and low blood sugar (if combined with insulin) remain under 1 in 1,000.
New 2025 safety updates added stronger wording about ileus (bowel obstruction)—still extremely rare but slightly higher with semaglutide.
Switching Between the Two
Many doctors switch patients who can’t tolerate one to the other. About 60-70% who fail Wegovy due to side effects do well on Mounjaro, and vice versa.
No washout period is needed—just start the new drug at the lowest dose the following week.
Cost and Insurance Impact on Choice
As of late 2025, both list around $1,300-$1,400 per month without insurance. Copays vary widely, but side-effect tolerance often decides when insurance pushes one over the other.
Summary
When comparing Wegovy vs Mounjaro side effects, Mounjaro causes more frequent but usually milder and shorter-lived GI issues, especially nausea and diarrhea. Wegovy has higher rates of constipation, gallbladder problems, and injection-site reactions. Both are very safe long-term for the vast majority, and most side effects fade after the first 3-4 months with proper dose escalation and diet tweaks.
FAQ
Which has worse nausea—Wegovy or Mounjaro?
Mounjaro has higher rates (44-51% vs 35-44%), but episodes are often milder and decrease faster after month three.
Is diarrhea or constipation more common?
Diarrhea is more common with Mounjaro; constipation is more common with Wegovy. Both usually resolve with time and fiber adjustments.
Do gallbladder problems happen more with one drug?
Yes, Wegovy shows roughly double the risk (1.6% vs 0.6-1.0%) in large 2025 studies, though still rare overall.
Can I switch if I can’t tolerate the side effects of one?
Absolutely—60-70% of people who stop one drug due to side effects tolerate the other well. Start low on the new one.
Do side effects ever go away completely?
For most users, yes—by month 6-12, fewer than 5% still have daily issues on either medication.
Dr. Hamza is a medical content reviewer with over 12+ years of experience in healthcare research and patient education. He specializes in evidence-based health information, medications, and chronic conditions. His reviews are grounded in trusted medical sources and current clinical guidelines to ensure accuracy, transparency, and reliability. Content reviewed by Dr. Hamza is intended for educational purposes and is not a substitute for professional medical advice.