Side effects are most noticeable in the first days after starting Mounjaro and after each dose increase, and they usually settle as your body adjusts. This is general information drawn from the official product information and the NHS — it isn't medical advice.
The most common side effects
Most Mounjaro side effects are digestive, because the medicine slows how quickly the stomach empties. The product information lists these as **very common** (affecting more than 1 in 10 people):
- Nausea
- Diarrhoea
- Vomiting
- Constipation
- Abdominal (tummy) pain
Other recognised effects
Effects listed as **common** (up to 1 in 10) include indigestion, bloating, burping, wind, acid reflux, reduced appetite, dizziness, tiredness and injection-site reactions. Burping with an unpleasant 'rotten egg' (sulphur) smell falls into this group and, like the others, tends to ease as your body settles.
How long they tend to last
For most people the roughest patch is the few days to couple of weeks after starting or stepping up a dose, easing as the body adjusts. Titrating slowly is the main way to keep this manageable — see our guide on managing side effects while titrating.
When to get medical help
Contact your prescriber or pharmacist if side effects are severe or persistent, or if you have signs of dehydration. Seek urgent medical attention for severe, persistent tummy pain that may spread to your back, as this can be a sign of pancreatitis. You can report any suspected side effect through the MHRA's Yellow Card scheme.