Mounjaro (tirzepatide) side effects and when to get help
Each Mounjaro side effect, grouped by how often it happens
The most common Mounjaro (tirzepatide) side effects are in the gut: feeling sick, diarrhoea, being sick, stomach pain and constipation each affect more than 1 in 10 people, alongside tiredness and feeling less hungry. They are most common when you first start and decrease over time in most people. A few are uncommon or rare but serious, and the signs to know by heart are severe stomach pain that does not go away and trouble breathing.
What are the common side effects of Mounjaro?
Most Mounjaro side effects affect the stomach and bowel. The table sets out every band as revised in August 2026.
| How often | Side effects listed |
|---|---|
| Very common (more than 1 in 10 people) | Feeling sick (nausea), diarrhoea, being sick (vomiting), stomach pain, constipation, tiredness, feeling less hungry, low blood sugar (hypoglycaemia) |
| Common (up to 1 in 10) | Indigestion, bloating, burping, gas, reflux, injection site reactions, a fast pulse, gallstones; in weight management also dizziness, low blood pressure, hair loss and an inflamed gallbladder (cholecystitis) |
| Uncommon (up to 1 in 100) | A changed sense of taste, slower stomach emptying, an inflamed pancreas (acute pancreatitis) |
| Rare (up to 1 in 1,000) | Severe allergic reactions (anaphylactic reaction, angioedema) |
Which Mounjaro side effects are rare but serious?
Two serious side effects need help quickly: acute pancreatitis, which is uncommon, and severe allergic reactions, which are rare. An inflamed pancreas can cause severe pain in the stomach and back that does not go away, with or without nausea and vomiting. Severe allergic reactions include anaphylaxis and angioedema, and breathing problems are one of their symptoms.
Pancreatitis stays uncommon. Even so, in January 2026 the MHRA strengthened its warnings on it for GLP-1 medicines and the dual GLP-1/GIP medicines such as Mounjaro, after UK reports that included necrotising and fatal cases, and treatment is not restarted once pancreatitis is confirmed.
When do Mounjaro side effects usually start and ease?
Gut side effects usually start in the first weeks and around each dose increase, then ease. Nausea, diarrhoea and vomiting occur mainly during dose escalation and decrease over time. A 2024 meta-analysis in Obesity Reviews, of trials in people with obesity, found side effects more frequent during dose titration and levelling off afterwards.
What the trials found
In the largest studies: SURMOUNT-3 and SURMOUNT-MAINTAIN, gut side effects were the most frequent, mostly mild to moderate, and came mostly during dose escalation.
- In a 72-week study of 579 adults with obesity. On Mounjaro, 39.7% felt sick and 31.0% had diarrhoea.
- In the same study, 23.0% on Mounjaro were constipated and 18.1% vomited, against 6.8% and 1.4% on placebo. About 1 in 10 on Mounjaro (10.5%) stopped because of side effects, against 2.1% on placebo.
- Across two more studies, the share who stopped because of stomach and gut side effects went up with the dose: 1.9% on 5 mg, 3.3% on 10 mg and 4.3% on 15 mg.
Mounjaro brought more stomach and bowel side effects, mostly at higher doses. It did not bring more serious side effects, or more episodes of very low blood sugar.
Do the usual tips for easing Mounjaro side effects work?
| Idea | Our view | Why |
|---|---|---|
| Ginger, peppermint or probiotic yoghurt ease the sickness and bloating | No evidence either way | There is no evidence on any of them for Mounjaro; gut side effects ease over time in most people anyway. |
| Magnesium eases side effects or restarts weight loss | No evidence either way | Constipation is very common; there is no evidence on magnesium for it. |
| Iron tablets on injection day prevent side effects | No evidence either way | There is no evidence on it, and no such step is part of using Mounjaro. |
| Plenty of fluids protects against dehydration when starting | Worth doing | Dehydration can happen when starting and may affect the kidneys. |
| Going up more slowly, or staying on a step, eases side effects | Makes sense but untested | Sickness and diarrhoea come mainly with dose increases, but there is no evidence comparing slower steps with the licensed ones. |
| Biotin or other hair supplements stop the shedding | No evidence either way | There is no evidence on them; hair loss is listed with no remedy attached. |
Sources
- Mounjaro KwikPen patient information leaflet
- GLP-1 and dual GLP-1/GIP receptor agonists: strengthened warnings on acute pancreatitis, including necrotising and fatal cases
- Mounjaro KwikPen summary of product characteristics
- Potent incretin-based therapy for obesity: a systematic review and meta-analysis
- Yellow Card
- Tirzepatide for weight reduction in adults with obesity after an intensive lifestyle intervention (SURMOUNT-3)
- Tirzepatide for maintenance of bodyweight reduction in people with obesity in the USA (SURMOUNT-MAINTAIN)
- Weight loss efficiency and safety of tirzepatide: a systematic review
- Subcutaneously administered tirzepatide vs semaglutide for adults with type 2 diabetes: a systematic review and network meta-analysis
