Mounjaro and weight management: a patient guide

Mounjaro is the brand name for tirzepatide. It is a prescription-only medicine that can be used to manage obesity or type 2 diabetes. The reason for treatment affects the assessment, prescribing criteria, and support that you need.

This guide gives general information about tirzepatide for weight management. It does not tell you whether the medicine is suitable for you.

How does tirzepatide work?

Tirzepatide acts on two hormone receptors called GLP-1 and GIP. These hormones are part of the systems that control appetite, digestion, and blood sugar.

For weight management, tirzepatide can reduce appetite and help you feel full for longer. It is used with a reduced-calorie diet and increased physical activity. It does not replace food, activity, sleep, or behavioural support.

Tirzepatide comes as an injection that you use once each week. A clinician will explain how to use and store it. Follow the patient information leaflet and the instructions from your prescriber.

Who can use it for weight management?

A clinician must assess you before they prescribe tirzepatide. They will usually check:

your height, weight, and body mass index (BMI)
health conditions that are related to your weight
your current and previous medicines
previous weight-management support
possible contraindications and medicine interactions
pregnancy, breastfeeding, and contraception where applicable

NHS and private prescribing criteria are not the same. NHS England is introducing access in phases, with initial access for people who have the highest clinical need. Local availability can also differ.

Meeting a BMI threshold does not automatically mean that treatment is suitable. The prescriber must consider your full medical history.

What side effects can occur?

Common side effects include nausea, vomiting, diarrhoea, constipation, stomach pain, and tiredness. Some people also get irritation at the injection site.

Tirzepatide can cause serious side effects. These are less common. The NHS advises people to call 111 if they think that they have a serious side effect. Severe, persistent pain in the stomach or back can be a sign of an inflamed pancreas and needs urgent assessment.

Read the leaflet supplied with the medicine. Speak to a pharmacist or prescriber if a side effect concerns you or does not improve. Do not increase the dose faster than instructed.

Pregnancy and contraception

Tirzepatide is not used during pregnancy. Tell your clinician if you are pregnant, plan to become pregnant, or are breastfeeding.

The MHRA advises people who use an oral contraceptive pill to add a barrier method, such as condoms, for four weeks after they start tirzepatide and for four weeks after each dose increase. You can also discuss a non-oral contraceptive method with a healthcare professional.

What happens if you stop treatment?

Speak to your prescriber before you stop. If you use tirzepatide for type 2 diabetes, stopping it can affect your blood sugar.

Weight management usually needs long-term support. Your clinician can help you plan food, activity, and other support if treatment stops. They will also review whether the medicine gives enough benefit and whether side effects are acceptable.

How can you get the medicine safely?

Only use tirzepatide that a qualified prescriber supplies after a proper consultation. Use a registered pharmacy. Do not buy it from social media, beauty salons, or a seller that does not ask for medical information.

The MHRA has warned about fake weight-loss medicines. A low price, no consultation, or a request for payment through an unusual method can be a warning sign.

Sources

Sources accessed on 2 September 2026.