Mounjaro Side Effects UK
The most common side effects of Mounjaro (tirzepatide) are stomach related: nausea, vomiting, diarrhoea, constipation and stomach pain. They are most likely in the first weeks and after each dose increase, and for most people they ease over time. A few side effects are serious and need urgent help.
When to get urgent help
This is at the top on purpose. If something feels seriously wrong, do not read on. Get help first.
Call 999 or go to A&E for severe stomach pain that does not go away, especially if it spreads to your back, with or without vomiting. This can be a sign of pancreatitis. Also call 999 for signs of a serious allergic reaction: swelling of the face, lips, tongue or throat, trouble breathing or swallowing, a rash that spreads fast, or feeling faint.
Contact NHS 111 or your GP the same day for pain in the upper right of your stomach with a fever, yellowing of your skin or eyes, or pale stools. These can be signs of a gallbladder problem. Also contact them if you cannot keep food or fluids down.
Do not wait for an online provider to reply. In an emergency, do not send a message and wait.
Wait, ask or act
|
What is happening |
What to do |
|
|---|---|---|
|
Wait |
Mild nausea, loose stools or constipation in the first weeks, or after a dose increase. These usually ease. |
Mention them at your next contact. Do not stop on your own. |
|
Ask |
Side effects that do not ease, or that stop you eating or drinking normally. |
Ask your prescriber or pharmacist. NHS 111 can tell you how urgent it is. |
|
Act |
Severe or lasting stomach pain, or signs of a serious allergic reaction. |
Call 999. |
Common side effects of Mounjaro
Most of the common side effects are in the stomach and gut, because Mounjaro slows how fast the stomach empties. The table shows how often each one happens, using the bands in the UK patient leaflet.
|
How common |
What it means |
Side effects |
|---|---|---|
|
Very common |
More than 1 in 10 people |
Nausea, diarrhoea, vomiting, constipation, stomach pain |
|
Common |
Up to 1 in 10 people |
Indigestion, bloating, burping, reflux, hair loss, dizziness, low blood pressure, injection site reactions |
|
Uncommon |
Up to 1 in 100 people |
Changes in taste, delayed stomach emptying, acute pancreatitis (see serious side effects) |
|
Rare |
Up to 1 in 1,000 people |
Severe allergic reaction (see serious side effects) |
The leaflet also lists tiredness and reduced appetite. Low blood sugar is mainly a risk if you also use insulin or a sulphonylurea. The leaflet gives some bands by use (type 2 diabetes or weight management), so check the current leaflet for your own situation.
Nausea and vomiting
The most common side effect. It is usually worst in the first weeks and after a dose increase. Smaller meals, eating slowly and avoiding rich or greasy food can help. Contact your prescriber or pharmacist if you cannot keep fluids down.
Diarrhoea
Loose stools are common early on. Drink plenty of fluids. Contact a prescriber if it lasts, or if you feel dizzy or very thirsty, as you may be dehydrated.
Constipation
One of the most searched Mounjaro side effects. Fluids, fibre and moving about can help. Ask a pharmacist before taking a laxative, and tell your prescriber if it lasts or comes with bad stomach pain.
Stomach pain, indigestion, reflux and bloating
Mild stomach discomfort is common. Pain that is severe, lasts, or spreads to your back is different. See When to get urgent help above.
Hair loss
Hair loss is listed as common. It is more often noticed with weight loss. Tell your prescriber or pharmacist if it bothers you.
Injection site reactions
Redness, itching or soreness where you inject is common. It is usually mild. Rotate the injection site as the leaflet explains, and tell your pharmacist if it is painful or spreads.
These are general tips, not medical advice. A pharmacist or prescriber can advise on your own situation. The patient leaflet is the authority for the medicine.
How long do Mounjaro side effects last?
Most people find stomach side effects are worst in the first weeks and then ease. They can come back for a short time after a dose increase, which is why the dose goes up in small steps.
|
When |
What to expect |
|---|---|
|
First weeks on the starting dose |
Nausea, loose stools or constipation are most likely. Most ease over a few weeks. |
|
After a dose increase |
A short return of the same effects is common. The dose goes up gradually, in steps of at least four weeks. |
|
After a missed dose |
The leaflet explains what to do. Do not take a double dose to catch up. |
|
After stopping |
The leaflet does not list side effects that start after stopping. If you feel unwell, speak to your prescriber or pharmacist. |
A bad week after an increase is not always a reason to stop. A prescriber can hold your dose or step it down. Do not change your dose on your own.
Serious side effects of Mounjaro
These are uncommon or rare. They are listed so you know what to look for, not because they are expected.
|
Serious side effect |
What to look for |
What to do |
|---|---|---|
|
Pancreatitis (uncommon) |
Severe stomach pain that does not go away, often spreading to the back, with or without vomiting |
Stop using Mounjaro and call 999 or get urgent medical help |
|
Severe allergic reaction (rare) |
Swelling of the face, lips, tongue or throat, trouble breathing, fast heartbeat, a rash that spreads fast |
Call 999 |
|
Gallbladder problems |
Pain in the upper right of the stomach, fever, yellow skin or eyes, pale stools |
Contact NHS 111 or your GP the same day |
|
Dehydration |
Lots of vomiting or diarrhoea, very thirsty, dark urine, dizzy |
Ask your prescriber or pharmacist. This can affect the kidneys |
|
Low blood sugar |
Shaky, sweaty, confused, mainly if you also use insulin or a sulphonylurea |
Tell your prescriber. They may need to lower the dose of your other medicine |
This is not the full list. Read the patient leaflet for everything it lists.
Questions people ask about Mounjaro side effects
Cancer. In studies in rats, tirzepatide caused tumours in the thyroid gland. It is not known whether this happens in people. Tell your prescriber if you have had thyroid problems or have a lump or swelling in your neck.
Eyes. The leaflet advises telling your doctor first if you have diabetic retinopathy or macular oedema. If your vision changes, tell your prescriber. Do not drive until it settles.
Liver. Liver problems are not listed among the side effects in the patient leaflet. Yellow skin or eyes and pale stools can be a gallbladder problem, so get advice the same day.
Mental health and anxiety. Low mood and anxiety are not listed as side effects in the patient leaflet. If you feel low or anxious, tell your prescriber or GP. Do not wait.
Heart and blood pressure. The leaflet lists dizziness and low blood pressure as common. A fast pulse is also listed. Stand up slowly, drink fluids, and tell your prescriber if you feel faint.
Long term side effects of Mounjaro
Mounjaro has been used for a limited time compared with older medicines, so long term safety data is still growing. The trials behind the UK approval followed people for about one to two years, so some effects over many years are not yet known.
Side effects such as gallstones and hair loss can appear during treatment as weight comes off. Report anything new or lasting to your prescriber, and report it through the Yellow Card scheme.
Side effects for different people
Mounjaro side effects in women
The leaflet gives one set of side effects for everyone. It does give extra advice for women. Mounjaro should not be used in pregnancy. If you use an oral contraceptive, the leaflet says to consider a barrier method, or a non oral method, for four weeks after starting and after each dose increase, because vomiting and diarrhoea can reduce how well the pill works.
Mounjaro side effects in men
The leaflet does not list different side effects for men. The side effects above apply to everyone.
Mounjaro side effects for people without diabetes
The side effects are mainly the same. Low blood sugar is mostly a risk for people with diabetes who also use insulin or a sulphonylurea. The leaflet shows some bands by use, so check the weight management information.
Side effects at different doses
Side effects are most likely when you start and after each increase, whether that is 2.5mg, 5mg, 7.5mg, 10mg or higher. There is no separate list for each dose. Your prescriber decides your dose and when to move up.
How to report a side effect
You can report a suspected side effect to the MHRA through the Yellow Card scheme. Patients can report, not only health professionals. Deal with any illness first, then report.
FAQs
Sources
- Mounjaro summary of product characteristics and patient information leaflet, electronic medicines compendium
- NHS 111 — when to use it, and how
- MHRA Yellow Card scheme — reporting a suspected side effect
- Background on the medicine itself: What is Mounjaro (Tirzepatide)?