Can Mounjaro Cause Blood Clots? UK Facts (October 2026)

01 · The core answer

Is a blood clot a Mounjaro side effect?

No: blood clots are not listed as a side effect in the Mounjaro KwikPen Summary of Product Characteristics or its patient information leaflet.¹¹³ The listed effects are overwhelmingly digestive.

Not being listed does not prove that nothing could ever happen to any individual. Anyone who develops a new symptom during treatment should tell their prescriber and can report it via the Yellow Card scheme.¹⁹

02 · Your next step

What should you do if you are worried?

If you have sudden, severe or unexplained symptoms, get medical help straight away; do not wait for a clinic appointment. Call 999 or go to A&E. A clot is a medical emergency whatever its cause, and the treating clinicians need to know every medicine you take.

If you are simply anxious, or have a personal or family history of clots, raise it in your consultation. Our free online consultation is reviewed by a GPhC-registered prescriber, who will weigh your full history before deciding whether treatment is suitable.

If you want more on a related question, our guide on whether Mounjaro is a blood thinner covers the other side of this topic.

03 · What the label lists

What the product information lists

Like all medicines, Mounjaro can cause side effects, and most are digestive.¹ The most common — affecting more than 1 in 10 people — are nausea, diarrhoea, vomiting, constipation and abdominal discomfort.¹ Side effects are most likely when starting treatment or moving up a dose, and for most people they ease within days to a few weeks as the body adjusts.

The serious side effects the label highlights are specific. Get medical help straight away for severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); for pain in the upper right abdomen, fever or yellowing of skin or eyes (possible gallbladder problems); or for signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing.¹¹³ Clots are not on that list.

The BNF entry for tirzepatide is another place prescribers check indications, dosing and safety information.¹¹

04 · Why people worry

Why people ask about Mounjaro and blood clots

News stories, social media posts and individual accounts can make a rare event feel common. Online reports are not evidence that a medicine caused something.

There is another reason the question comes up. Anyone starting a new injectable medicine is likely to notice every new sensation in their body for the first few weeks. Many ordinary things, such as a bruise at an injection site, a tired leg or a tight chest from anxiety, can feel worrying. Most have simple explanations, but the safe approach is to ask rather than guess.

It also helps to remember that people who take weight-management medicines are a very large and varied group, and clots happen in the general population for many reasons unrelated to any medicine. When two things happen at the same time, it does not mean one caused the other. That is why regulators look at patterns across many people rather than single stories, and why the Yellow Card scheme exists.

05 · Symptoms and urgent help

Signs of a clot and when to get urgent help

The NHS publishes detailed, regularly updated advice on deep vein thrombosis and pulmonary embolism.

The practical rule is simple. Any sudden, severe or unexplained symptom, especially one that is one-sided, rapidly worsening or affects your breathing, needs urgent assessment. Call 999 or go to A&E instead of waiting to see whether it passes. Tell the clinician you are taking Mounjaro and when you last injected.

The same urgency applies to the serious effects the label does list. Seek immediate medical help for severe, persistent stomach pain that may spread to your back, pain in the upper right abdomen with fever or yellowing skin or eyes, or swelling of the face or throat with difficulty breathing.¹ If you are unsure which category a symptom falls into, get medical help straight away.

If you notice blood in your stool or urine, that is a different question with different causes. Our guides on blood in stool and blood in urine explain what to do.

06 · Before you start

What to tell your prescriber before you start

Share your full medical history and medicine list during consultation. Mounjaro is not suitable for everyone. You should not take it if you are allergic to tirzepatide or any of its ingredients, and it should not be used during pregnancy or while trying to conceive. Mounjaro must not be used during pregnancy, and it should be stopped at least one month before trying to conceive. If you become pregnant during treatment, stop the medicine and tell your prescriber promptly. Your prescriber takes extra care, or may recommend against treatment, if you have a history of pancreatitis, severe gut or digestive disease, diabetic retinopathy or gallbladder problems.¹

Your history of blood clots also matters. If you have ever had a clot, are on treatment for one, take any blood-related medicine, or have a close relative with a clotting condition, say so. The prescriber can then decide whether treatment is appropriate and how closely to follow you up.

Also mention any medicines you take for diabetes. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion), because your prescriber may need to adjust those medicines.¹

Our aftercare includes ongoing monthly reviews, so you have a route to raise new concerns with the prescribing team. Repeat orders re-check suitability, and nothing ships automatically.

07 · Reporting a concern

Reporting a suspected side effect

You can report any suspected side effect, including one not listed in the leaflet, to the MHRA through the Yellow Card scheme.¹⁹ Reports from patients and healthcare professionals are how regulators spot patterns that trials were too small to show.

A report does not mean the medicine caused the event. It simply gives the regulator information to review alongside everything else. If a clinician treats you for any serious event while you are on Mounjaro, ask whether they will report it, and consider reporting it yourself.

Our Mounjaro comes through official LillyDirect supply, direct from Eli Lilly's UK distribution, and we are GPhC-registered (9012878).

08 · Wider health effects

What trials do show about health beyond weight

In trials, weight loss on tirzepatide came with average improvements in waist size, blood pressure, cholesterol and blood-sugar measures, and most participants with prediabetes returned to normal blood-sugar levels.² These are trial-average secondary outcomes, not promises, and they do not tell you anything about clot risk specifically.

Blood pressure sometimes comes up alongside this question; see our guide on whether Mounjaro can cause blood pressure to drop.

09 · Staying well on treatment

Staying well while on Mounjaro

Most of what keeps you well on treatment is ordinary good practice. Eat smaller meals slowly, stop at the first feeling of fullness, favour plain lower-fat foods while adjusting, stay well hydrated and avoid lying down straight after eating.¹ If nausea or vomiting is persistent or you cannot keep fluids down, contact your clinical team — dehydration needs prompt attention.

Keep gentle activity going, because treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them. Most side effects appear in the first days after starting or increasing a dose, peak early and settle as your body adapts. If a new dose is hard to tolerate, prescribers can hold the current dose longer before stepping up.

For a practical overview of safety habits, see our blood clot risk safety tips. Our complete UK guide to Mounjaro and clots brings the points together.

10 · Stopping and clearance

How long does Mounjaro stay in your system, and what happens if you stop?

Tirzepatide has a half-life of about five days, so after a final dose it takes roughly four to five weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹ Mounjaro manages weight; it does not cure the biology behind it. In SURMOUNT-4, people who stopped tirzepatide after 36 weeks regained on average 14% of body weight over the following year, while those who continued treatment lost a further 5.5% on average. Stopping should always be planned with your prescriber, with diet and activity habits ready to carry the load.

This matters if you ever need to tell a hospital team what you are taking. Tell them the date of your last injection even if you have stopped, because the medicine will still be present for a while. Do not stop treatment on your own because of a general worry; talk to your prescriber first, and seek urgent help if you have symptoms that frighten you.

If you donate blood and want to know how treatment fits, see blood donation and Mounjaro.