Is Mounjaro Safe?

Medically reviewed by
Dr Brenda IkejiLast reviewed: 08 Jan 2025
All medications available in the UK undergo clinical trials to ensure their safety, and Mounjaro is no exception. Mounjaro was approved by the Medicines and Healthcare Products Regulatory Agency (MHRA) after undergoing 7 different studies, including almost 10,000 participants over 56 to 72 weeks.
The results of these trials found that Mounjaro is safe and effective when prescribed to those who meet the suitability criteria. However, as with any medication, there is still a chance of side effects. This guide looks into the safety of Mounjaro in clinical trials, and how you can take it safely.
Is the weight loss injection Mounjaro safe?
Yes, when Mounjaro is prescribed and used correctly, it is a safe and effective weight loss treatment. Your doctor will consider your medical history, including past and current conditions and medications, and your body mass index (BMI) when prescribing Mounjaro.
Mounjaro may not be safe if you take it without a prescription, and as with any medication, there is a chance of serious side effects. Most side effects are mild and go away over time but being aware of side effects and reporting them to your doctor can help keep you safe during your treatment.
The Mounjaro dosage schedule is also in place to introduce the active ingredient (tirzepatide) into your body slowly, reducing the chance of side effects. You can stay on a lower dose for longer if you’re worried about side effects, and are still seeing the benefits of the medication and losing weight.
If you're concerned or believe you might be experiencing serious side effects at any point in your treatment, please call 111 or go to A&E as soon as possible.
from £179.00

No results found.
Please check your spelling or try another treatment name.
Safety profile of Mounjaro
Mounjaro has been thoroughly tested and approved for use by the MHRA for both type 2 diabetes and weight loss.
Type 2 diabetes trials
Mounjaro was reviewed closely in 5 clinical trials, known as SURPASS 1 to 5, involving 6,263 patients. The study results found that Mounjaro significantly decreased blood sugar levels for up to 2 years. During these trials, it was also found that Mounjaro helped people to lose weight.
Weight loss trials
Mounjaro was then studied in the SURMOUNT 1 and 2 clinical trials as a weight loss medication. This involved 3,477 overweight or obese patients with and without diabetes. The results found significant reductions in body weight compared to a placebo, regardless of the patient's age, race, ethnicity, blood sugar levels, and baseline BMI.
Side effects
For weight management, the most common Mounjaro side effects noted in clinical trials were those affecting the gastrointestinal (GI) tract: nausea, vomiting, diarrhoea and constipation. These were mostly mild (61%) to moderate (34.4%) and usually seen after the dose was increased and improved over time. 2.1% of patients stopped taking tirzepatide due to GI side effects.
Mounjaro benefits
As Mounjaro can help reduce your BMI, it can lead to a reduction of developing weight-related medical conditions, or an improvement in conditions you already have, including:
- diabetes
- cardiovascular disease
- high blood pressure
- PCOS
- high cholesterol
"Your safety is, and always will be, our top priority. This is why our licensed and registered UK doctors thoroughly review every consultation we receive before prescribing, to ensure appropriate and safe treatment. This is also why we ask for photos of your current weight, as Mounjaro should only be prescribed to those who meet the BMI requirements. For further information on Mounjaro and other weight loss medications, please see our weight loss FAQs. You can also message a doctor for free advice if you’re taking Mounjaro and have any worries or concerns."
Common side effects of Mounjaro
The most common Mounjaro side effects (may affect up to 1 in 10 people) are:
- nausea
- vomiting
- diarrhoea
- constipation
Mounjaro side effects are usually not severe and are most likely to happen when starting treatment or increasing your dose.
Knowing what to eat on Mounjaro can reduce the likelihood and severity of GI side effects. For example, processed, fatty, or greasy foods can make them worse, while nutritious, healthy, and small meals could improve them.
Serious side effects of Mounjaro
Uncommonly (may affect up to 1 in 100 people), Mounjaro can cause an inflamed pancreas (acute pancreatitis). Symptoms include long-lasting and severe pain in the stomach and back.
Rarely (may affect up to 1 in 1,000 people), Mounjaro can cause a severe allergic reaction (anaphylaxis or angioedema). Symptoms include:
- problems breathing
- swelling of the face and lips
- difficulty swallowing
These side effects are serious, and you or someone else must speak to a doctor or call 999 straight away.
➤ For a full list of potential Mounjaro side effects, including what to do if you get them and how to manage them, read our Mounjaro side effects guide.
Mounjaro risks
Mounjaro risks are most likely if you have a medical condition or take a medication that may interact with it, but your doctor will make sure this isn’t an issue before prescribing it.
Mounjaro risks may be increased if you:
- do not take it properly, such as doubling your dose or taking it more than once a week
- do not obtain a prescription from a doctor
- choose to buy Mounjaro pens from an unregulated website, as the pens could be fake
Mounjaro is not suitable for everyone. You could be at risk of health problems if you do not get a prescription from a doctor, or if you do not let your doctor know about a condition or treatment you’re taking that could interact with Mounjaro.
What to do if you take too much Mounjaro
If you use more Mounjaro than you have been prescribed, talk to your doctor or call 111 straight away. Taking too much may cause low blood sugar (hypoglycaemia), nausea, and vomiting.
Who should not take Mounjaro for weight loss?
You should not use Mounjaro if you are:
- allergic to any ingredients in the medication
- pregnant
- planning to get pregnant
- breastfeeding
Mounjaro may also not be appropriate if you:
- have severe problems with food digestion, such as severe gastroparesis (a disorder that slows or stops the movement of food from your stomach to your small intestine)
- have ever had pancreatitis – Mounjaro can also cause this
- have a problem with your eyes, such as diabetic retinopathy or macular oedema – Mounjaro may make your symptoms worse
- are diabetic and are using sulphonylurea or insulin – low blood sugar can occur so your doctor may need to change your dose of these medications
- are due to have surgery under anaesthesia
If you’re not sure, speak to your doctor.
How to use Mounjaro safely
To use Mounjaro safely you need to know how to inject it properly and how to increase your dosage. Your doctor will provide full instructions on this.
Injecting Mounjaro safely
The 3 main injection sites are your abdomen, upper arms (if you can get someone to do it for you), and upper legs. Find out more about injecting Mounjaro safely in our Mounjaro injection guide.
Following the Mounjaro dosage schedule
The Mounjaro dosage schedule involves increasing your dose every 4 weeks until you reach a maintenance dose that works for you. The starting dose is always 2.5mg once a week, and the maximum maintenance dose is 15mg.
You can also use a maintenance dose of 5mg or 10mg. You may want to stay on a lower dose of tirzepatide because of side effects, or because you’re happy with your weight loss results and do not want to take a higher dose. If you change your mind at any point, you can increase your dose as long as it’s been at least 4 weeks on your current dose.
Our doctor guide on Mounjaro dosages explains how and why you’ll increase your dose, and what to do if you get side effects.
Frequently asked questions
Is Mounjaro safe for heart patients?
Yes, Mounjaro is safe for heart patients and your doctor may recommend using a weight loss medication like Mounjaro if you’re overweight to help improve your condition or reduce the risk of serious events. As well as reducing BMI, which can improve heart health, studies have shown that tirzepatide can:
- lower the risk of inflammatory markers associated with cardiovascular events (like a heart attack)
- lower the risk of death or worsening heart failure and improve health in patients with heart failure with preserved ejection fraction
Is Mounjaro safe for kidneys?
Mounjaro is safe for kidneys in most cases, although if you lose a lot of fluids because of vomiting, nausea, or diarrhoea, it may lead to a decrease in kidney function. It’s important to stay hydrated and speak to your doctor if you’ve got severe symptoms, especially if you have kidney problems.
Mounjaro also contains benzyl alcohol, so you should ask your doctor for advice on taking it if you’ve got liver or kidney disease. Large amounts of benzyl alcohol can build up in your body and may cause metabolic acidosis.
Is Mounjaro safe while pregnant?
No, Mounjaro is not safe while pregnant or if you’re trying to become pregnant. This is because it’s not known how much of the active ingredient can be passed to an unborn baby or what effect this could have.
When using Mounjaro alongside an oral contraceptive pill, the manufacturer recommends using another form of contraception, such as a condom, for 4 weeks after starting Mounjaro, and for 4 weeks after each dose increase. Some side effects, like severe vomiting or diarrhoea, could affect how well your contraceptive pill works, especially if you vomit soon after taking it.
Is Mounjaro safe for long-term weight loss?
Yes, Mounjaro is safe for long-term weight loss and can be taken for years with a doctor’s supervision. Clinical studies followed patients for 72 weeks when taking Mounjaro for weight loss.
You might need to stop taking Mounjaro if you get side effects that do not go away or are severe. Your doctor will also decide whether to stop treatment if you’ve been taking your maintenance dose for 6 months and have not lost at least 5% of your starting weight.
from £179.00

No results found.
Please check your spelling or try another treatment name.

Brenda studied medicine at St Georges University of London and has most recently worked in John Radcliffe Oxford University Hospitals, covering acute and general medicine.
Meet our doctorsLast reviewed: 08 Jan 2025
-
Four-dose Mounjaro “KwikPen” approved by MHRA for diabetes and weight management, Gov.uk [accessed 31 December 2024]
-
Mounjaro KwikPen 2.5mg solution for injection in pre-filled pen (SmPC, emc [accessed 31 December 2024]
-
Mounjaro KwikPen 2.5mg solution for injection in pre-filled pen (PIL), emc [accessed 31 December 2024]
-
The Cardiovascular Effect of Tirzepatide: A Glucagon-Like Peptide-1 and Glucose-Dependent Insulinotropic Polypeptide Dual Agonist, PubMed [accessed 31 December 2024]
-
Tirzepatide for Heart Failure with Preserved Ejection Fraction and Obesity, The New England Journal of Medicine [accessed 31 December 2024]




(Reviews are for ZAVA UK)


GMC: 7074021

GMC: 6149061

GMC: 7085115

