Mounjaro Side Effects

Common side effects

Mounjaro (tirzepatide) is a dual agonist that acts on both GLP-1 and GIP receptors. Because of this dual action you see a comparable, but sometimes somewhat more intense, digestive effect than with pure GLP-1 medicines such as Ozempic.

The most frequently reported side effects in the SURMOUNT studies: nausea (up to 33 percent at 15 mg), diarrhoea (23 percent), constipation (17 percent), reduced appetite (10 percent), vomiting (14 percent), abdominal pain, fatigue and injection-site reactions.

Important to know: the intensity of side effects is dose-dependent. At 2.5 mg they are usually mild, at 15 mg considerably more intense. Slow titration (one step up every 4 weeks) prevents severe symptoms for most people.

Mounjaro versus Ozempic and Wegovy

In direct head-to-head comparisons (SURPASS-2, SURMOUNT vs SELECT), the side-effect profile of tirzepatide and semaglutide was comparable: nausea, diarrhoea and constipation occurred equally often. Discontinuations due to side effects were slightly lower or equal with Mounjaro.

A clinically notable difference: at the highest dose (15 mg tirzepatide vs 2.4 mg semaglutide), tirzepatide caused comparable symptoms but considerably more weight loss. The benefit/side-effect ratio is therefore more favourable for many patients.

People who previously tolerated Ozempic or Wegovy poorly sometimes tolerate Mounjaro better, and vice versa. There is no hard rule as to which medicine causes the fewest symptoms in an individual.

Rare but serious risks

Pancreatitis: rare (<0.5%), but serious. Symptoms: severe, radiating abdominal pain with nausea. Stop immediately and consult a doctor.

Gallstones and gallbladder inflammation: increased risk with rapid weight loss (more often with tirzepatide because of the larger change in weight). Symptoms: pain under the right rib cage, nausea, fever.

Medullary thyroid carcinoma: seen in animal studies, not shown to be increased in humans. Contraindicated in hereditary MEN2 or a personal/family history of medullary thyroid carcinoma.

Hypoglycaemia: fairly rare when used without insulin or a sulfonylurea, but possible. In patients with diabetes, other medication needs to be adjusted.

Practical tips per symptom

Nausea: eat smaller portions, avoid fatty and very sweet food, no overly full meals just before bed. Ginger tea can help. Anti-emetics (such as metoclopramide) only after consulting your doctor.

Diarrhoea: ORS or an electrolyte drink if you lose a lot of fluid, BRAT diet (banana, rice, apple sauce, toast), temporarily avoid coffee and alcohol. Longer than 3 days: call your doctor.

Constipation: extra fibre (psyllium, chia), at least 2 litres of water per day, daily exercise, macrogol as advised by your doctor if necessary.

Reflux and heartburn: sit upright after eating, no spicy food just before sleeping, a short course of an acid reducer (esomeprazole) as advised by your doctor if necessary.

When to get in touch immediately

Call 112 (the Dutch emergency number) or go to the emergency department immediately for: severe radiating abdominal pain, blood in stool or vomit, jaundice (yellow skin/eyes), severe allergic reaction (swollen throat/lips), palpitations with dizziness.

Call your doctor within 24 hours for: diarrhoea or vomiting lasting longer than 3 days, signs of dehydration, sudden marked loss of vision, persistent pain in the upper right abdomen (gallbladder), unexplained severe fatigue or muscle weakness.

Monitoring at Go Leaner

When starting Mounjaro we carry out extensive blood screening (kidney, liver and thyroid function, lipase, HbA1c, lipids). During the titration phase, consultations follow every 4 to 6 weeks, then every six months or sooner if you have symptoms.

Via the app you can ask questions 24/7. If side effects persist, we adjust your schedule: longer adjustment per dose, a temporary pause or switching to semaglutide. Treatment is not imposed unilaterally but steered in consultation.