Mounjaro vs Wegovy Side Effects: What to Expect (2026)

Do Mounjaro and Wegovy have the same side effects? Both are GLP-1 receptor agonists and share similar gastrointestinal side effects, but there are important differences in severity, frequency, and how long they last. This guide compares them based on clinical trial data and real-world experience.

Common side effects compared

Both medications cause gastrointestinal side effects, especially during dose escalation. These typically improve after 4–6 weeks at each new dose level.

| Side effect | Mounjaro (tirzepatide) | Wegovy (semaglutide) | |-------------|----------------------|---------------------| | Nausea | 24–33% (dose-dependent) | 44% | | Diarrhoea | 12–21% | 30% | | Constipation | 6–11% | 24% | | Vomiting | 6–12% | 25% | | Abdominal pain | 5–8% | 11% | | Decreased appetite | 10–14% | 9% | | Injection site reactions | 3–7% | 4% |

When do side effects start?

Side effects are most common:

• Weeks 1–4 of each new dose: This is when your body adjusts. Nausea is usually worst during this period.
• Dose escalation phases: Both medications gradually increase the dose. Mounjaro escalates through 6 doses (2.5mg to 15mg), Wegovy through 5 (0.25mg to 2.4mg).
• After large meals: Eating smaller, more frequent meals can reduce nausea significantly.

Most patients find side effects settle within 4–6 weeks of reaching their maintenance dose.

Serious side effects

Both medications carry rare but serious risks. These are listed in the prescribing information and should be discussed with your clinician:

Pancreatitis — rare (under 1%) with both medications. Stop treatment and seek medical attention if you experience severe, persistent abdominal pain.

Gallbladder problems — rapid weight loss from any cause can increase the risk of gallstones. This affects both medications equally.

Thyroid tumours — animal studies showed increased thyroid C-cell tumours with GLP-1 agonists. This has not been confirmed in humans, but both medications carry a precautionary warning. Do not use if you have a personal or family history of medullary thyroid carcinoma or MEN2.

Hypoglycaemia — rare when used alone, but possible if combined with insulin or sulfonylureas.

Tips for managing side effects

1. Eat smaller meals — the most effective way to reduce nausea
2. Stay hydrated — important if you experience diarrhoea or vomiting
3. Avoid fatty foods — GLP-1 medications slow digestion; high-fat meals worsen nausea
4. Take the injection in the evening — some patients find this reduces daytime nausea
5. Don't skip doses — inconsistent dosing can increase side effects
6. Talk to your prescriber — they can slow dose escalation if side effects are severe

Which has fewer side effects?

Based on clinical trial data, Mounjaro generally causes fewer gastrointestinal side effects than Wegovy, despite producing more weight loss. This may be because Mounjaro's dual GIP/GLP-1 mechanism has a slightly different effect on the gut compared to semaglutide's GLP-1-only action.

However, individual responses vary significantly. Some patients tolerate Wegovy well but struggle with Mounjaro, and vice versa. If side effects are unmanageable on one, switching to the other is a reasonable option.

Compare prices

Both medications are available from GPhC-registered UK pharmacies. Prices are updated daily.

Related guides

• Mounjaro vs Wegovy: Which Is Better? — full head-to-head comparison
• How Much Does Mounjaro Cost? — pricing by dose
• How Much Does Wegovy Cost? — Wegovy pricing guide
• GLP-1 Weight Loss Injections: Complete Guide — all options explained