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Tirzepatide side effects

Tirzepatide side effects

Tirzepatide is the medicine inside Mounjaro. Stomach upsets head the list of side effects and peak after each dose increase. A few rarer effects need fast action.

By Gary Atmos, Penzilla Editorial Team. Last reviewed 8 October 2026.

Side effects ranked by frequency

Most frequent (over 1 person in 10): nausea, diarrhoea, vomiting, constipation.
Common (up to 1 in 10): stomach ache, indigestion, bloating, burping, wind, heartburn, fatigue, dizziness, hair thinning, low blood pressure, soreness where you inject, allergic reactions.
Uncommon (up to 1 in 100): gallstones, gallbladder inflammation, acute pancreatitis, faster heart rate.

Frequencies come from the product licence.

Pancreatitis: the January 2026 warning

The MHRA tightened the wording on acute pancreatitis for the whole GLP-1 family on 29 January 2026, tirzepatide included. The condition is uncommon and sometimes severe.

Red flag. Strong, lasting stomach pain, sometimes reaching through to your back, needs same day medical attention. The MHRA names this as the main warning sign of pancreatitis. Tell the MHRA about any suspected reaction on the Yellow Card site.

If you take the contraceptive pill

Tirzepatide slows the stomach, which can lower the amount of pill your body absorbs. The licence asks you to use condoms or another barrier as well for four weeks from your first injection, and for four weeks after every increase. Stop Mounjaro if you become pregnant.

If you take diabetes medicines

Insulin and sulfonylureas combined with tirzepatide raise the risk of low blood sugar. The prescriber may cut their doses.

Easing stomach side effects

Smaller portions help most. Eat slowly and stop at the first sign of fullness. Go easy on rich, greasy food in the week after an increase. Keep fluids up. If a new dose hits hard, ask the prescriber about staying put for another four weeks.

A week by week pattern

Stomach effects tend to appear in the first few days after an injection and ease before the next. They return, usually milder, after each increase. By the time you have held a dose for a month, most have settled.

Operations and anaesthetics

Tirzepatide keeps food in the stomach for longer. Tell your surgical team you take Mounjaro well before any procedure with sedation or anaesthetic.

Trial drop out rates

Between 4 and 7 in 100 people stopped tirzepatide because of side effects in SURMOUNT-1, against under 3 in 100 on placebo.

Mounjaro dose chart. Mounjaro prices.

Questions people ask

What is the most common side effect of tirzepatide?

Nausea, followed by diarrhoea, vomiting and constipation.

Do tirzepatide side effects wear off?

For most people they fade as the body settles on each dose.

Does tirzepatide affect the pill?

Yes. Add a barrier method for four weeks after starting and after each increase.

Should I tell my surgeon I take Mounjaro?

Yes, in advance. The medicine slows stomach emptying.

Where do I report a side effect?

On the MHRA Yellow Card site or app.

Sources

Eli Lilly, Mounjaro KwikPen Summary of Product Characteristics (electronic medicines compendium)
Jastreboff AM and colleagues, SURMOUNT-1, New England Journal of Medicine, 2022
MHRA Drug Safety Update, GLP-1 and dual GLP-1/GIP receptor agonists: strengthened warnings on acute pancreatitis, 29 January 2026
MHRA, Yellow Card reporting site