Mounjaro
Mounjaro side effects: what to expect and how to manage them
6 min read · Updated August 2026 · Reviewed by the Miva clinical team
Most people who start Mounjaro (tirzepatide) notice some digestive side effects, especially in the first weeks after starting and after each dose increase.
They're usually mild to moderate and settle as your body adjusts. Knowing what's expected — and what needs a clinician — makes the first few months much easier.
The most commonly reported side effects
Tirzepatide slows how quickly the stomach empties and acts on appetite signals in the brain. That mechanism is also why most side effects are gastrointestinal.
- Nausea, particularly in the 24–72 hours after an injection
- Constipation or diarrhoea
- Indigestion, reflux and burping
- Reduced appetite and feeling full very quickly
- Tiredness, especially while eating less
- Redness, itching or a small lump at the injection site
How long do side effects usually last?
Side effects tend to be at their strongest in the first week of a new dose and ease over the following two to three weeks. This is the main reason tirzepatide is titrated slowly, starting at 2.5 mg for four weeks rather than starting at a therapeutic dose.
If a dose step is consistently hard to tolerate, staying at your current dose for longer is a legitimate option — reaching the maximum dose is not the goal, reaching an effective and tolerable dose is.
Practical ways to reduce nausea
- Eat smaller portions and stop at the first sign of fullness rather than finishing the plate
- Choose lower-fat, blander foods on the day of and after your injection
- Sip fluids steadily through the day instead of large amounts with meals
- Keep protein intake up — it protects muscle while you're eating less
- For constipation: more fibre, more fluid, daily movement, and speak to your pharmacist about a suitable laxative
- Ask about staying on your current dose an extra few weeks before stepping up
Less common but serious — get medical help
These are uncommon, but they need prompt attention rather than watchful waiting.
- Severe, persistent abdominal pain that may spread to your back, with or without vomiting (possible pancreatitis) — seek urgent care
- Signs of gallbladder problems: pain in the upper right abdomen, fever, yellowing of the skin or eyes
- Persistent vomiting or diarrhoea leading to dehydration
- Signs of low blood sugar if you also take insulin or a sulfonylurea: shakiness, sweating, confusion
- Any allergic reaction — rash, swelling of the face or throat, difficulty breathing (call 911)
Who shouldn't take tirzepatide
Tirzepatide isn't suitable for everyone. Your assessment asks about these specifically, and a clinician will decline treatment where it isn't safe.
- A personal or family history of medullary thyroid carcinoma, or MEN2 syndrome
- A history of pancreatitis
- Pregnancy, planning pregnancy, or breastfeeding
- Active severe gastrointestinal disease, including gastroparesis
- A current or past eating disorder
Frequently asked questions
Does Mounjaro cause hair loss?
Hair shedding reported during treatment is usually telogen effluvium linked to rapid weight loss and lower nutrient intake rather than a direct drug effect. Losing weight at a steadier pace and keeping protein, iron and overall calories adequate reduces the risk, and it's typically temporary.
How long do Mounjaro side effects last?
Most digestive side effects are worst in the first week after starting or increasing a dose and settle within two to four weeks. Side effects that keep getting worse, or that stop you eating and drinking normally, should be reviewed by a clinician.
Can I drink alcohol on Mounjaro?
There's no absolute interaction, but alcohol can worsen nausea and reflux, adds calories, and can lower blood sugar — a particular consideration if you also take insulin or a sulfonylurea. Many people find they want much less alcohol on treatment.
Does Mounjaro need to be refrigerated?
Store pens in the fridge at 2–8°C. An unopened pen can be kept at room temperature (below 30°C) for a limited period — check the leaflet in your pack for the exact number of days, and never freeze a pen or use one that has been frozen.
Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only medicines in Canada. This page is general information, not medical advice — a Canadian-licensed clinician reviews every assessment and decides whether treatment is suitable for you.
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