On this page
- Before You Start
- Quick Answer
- What Does Mounjaro Do?
- How Is It Usually Started?
- Your Weekly Injection
- Looking After Your Pen
- What Might You Notice First?
- Do Not Aim To Eat As Little As Possible
- Six Things To Do From Week One
- What If I Miss A Dose?
- If Your HRT Includes Progesterone Tablets
- Important Safety Reminders
- When To Seek Urgent Help
- Where To Read Next
- Dr Mel’s Notebook
- Key Messages
- Useful Sources
Before You Start
This page is general education for people who have been prescribed Mounjaro. It does not replace advice from your own prescriber, pharmacist, GP practice or specialist team.
Last reviewed: 15 July 2026
Mounjaro can be a very useful medicine, but it works best when it is used as part of a bigger plan for health. The aim is not to eat as little as possible. The aim is to use the quieter appetite to build habits that your future self can keep.
Quick Answer
Mounjaro is a once-weekly injection. It can reduce appetite, increase fullness and quieten food cravings. Many people find this helpful, but side effects are common, especially when starting or increasing the dose.
The most important things to remember are: eat slowly, stop at comfortably full, drink enough, prioritise protein and fibre, and ask for advice if symptoms are severe or you cannot eat or drink enough.
What Does Mounjaro Do?
Mounjaro contains tirzepatide. It helps regulate appetite and can make you feel fuller and less hungry. Many people describe this as turning down the “food noise”.
That can create space to build healthier habits around food, movement, sleep and self-care. The medication changes your appetite. The habits change your future.
How Is It Usually Started?
Mounjaro is usually started at 2.5 mg once a week for four weeks. The dose is then usually increased to 5 mg once a week. If needed, your prescriber may increase it in 2.5 mg steps, with at least four weeks on each dose.
Do not change your dose unless your prescriber has told you to. If side effects are still difficult or are affecting what you can eat or drink, contact the prescribing team before moving up. The next increase can be delayed until symptoms have settled or become manageable.
Your Weekly Injection
- Use Mounjaro on the same day each week, at any time of day and with or without food.
- Inject it under the skin of your abdomen or thigh. The back of the upper arm can also be used if another person gives the injection.
- Choose a different injection site each week, even if you use the same general area.
- Read the official Instructions for Use supplied with your pen before your first injection.
Looking After Your Pen
Each Mounjaro KwikPen contains four doses. A small amount of medicine may remain after all four doses have been given. Do not try to extract or inject this remaining medicine. Dispose of the pen after the fourth dose as instructed by your pharmacist or prescribing team.
Store unused pens in a refrigerator between 2°C and 8°C and do not freeze them. After first use, a pen can be kept below 30°C for up to 30 days and must then be discarded. Do not use a pen that has been frozen, damaged, cloudy, discoloured or contains particles.
What Might You Notice First?
Meals may feel too big. This is expected, but poor nutrition is not the goal.
Eating slowly helps you notice when you are comfortably full.
Feeling sick is common, especially early on or after dose increases.
Your gut may take time to adjust, especially if food and fluid intake changes.
Rich meals, large meals and eating quickly can make this worse.
This can sometimes be linked to eating too little or not drinking enough.
Do Not Aim To Eat As Little As Possible
Reduced appetite is expected. Poor nutrition is not.
Your body still needs protein, fibre, carbohydrates, healthy fats, vitamins, minerals and fluid. Think of Mounjaro as making your plate smaller, not less nutritious.
Six Things To Do From Week One
Pause during meals and stop when comfortably full.
Include protein when you eat: yoghurt, eggs, beans, fish, chicken, tofu, nuts or seeds.
Small sips through the day can be easier than large drinks.
Oats, beans, lentils, fruit, vegetables and wholegrains help your gut.
Walking helps health, mood, constipation and confidence.
Choose one habit you would like to keep long term, not ten at once.
What If I Miss A Dose?
The patient leaflet says that if it has been 4 days or less since the missed dose, use it as soon as you remember, then continue on your usual day. If it has been more than 4 days, skip that dose and take the next one on your usual day.
Do not take two doses to make up for a missed dose. There should be at least 3 days between doses.
If Your HRT Includes Progesterone Tablets
Mounjaro slows stomach emptying, so it may affect how oral medicines are absorbed. There is not yet enough research to know exactly how much this affects oral progesterone or other oral progestogens used as part of HRT.
Specialist menopause guidance recommends reviewing HRT that includes an oral progesterone or progestogen when Mounjaro is started and after dose increases. Tell both your Mounjaro prescriber and the clinician responsible for your HRT so they can consider whether your treatment remains suitable for you.
Do not stop or change your HRT yourself. Ask for medical advice if you develop new or unexpected vaginal bleeding.
Important Safety Reminders
- Tell your prescriber if you have had pancreatitis, severe digestive problems, diabetic eye disease, or complex medical conditions.
- If you use insulin or a sulphonylurea for diabetes, you may need extra advice because low blood sugar can occur.
- Make sure your prescribing team knows about all the medicines you take. Mounjaro can affect how quickly some oral medicines are absorbed, and medicines such as warfarin or digoxin may need closer monitoring when treatment starts or the dose changes.
- If you use oral contraception, use an additional barrier method, such as condoms, for 4 weeks after starting and for 4 weeks after each dose increase. Alternatively, ask about changing to a non-oral method.
- Tell your surgical or anaesthetic team that you take Mounjaro if you are having surgery or sedation.
- Mounjaro should not be used during pregnancy. If you think you may be pregnant, stop taking it and contact a healthcare professional straight away. Stop Mounjaro at least 1 month before a planned pregnancy.
- If you are breastfeeding or planning to breastfeed, ask your prescriber for individual advice before using or continuing Mounjaro.
When To Seek Urgent Help
Use urgent medical advice if you have:
- severe, persistent stomach pain, especially if it goes through to your back, with or without vomiting
- repeated vomiting or you cannot keep fluids down
- signs of dehydration such as passing very little urine, fainting, confusion or extreme weakness
- swelling of the lips, tongue or throat, breathing difficulty, collapse or severe allergic symptoms
- severe right-sided upper tummy pain, fever, yellowing of the skin or eyes, or dark urine
If you develop severe, persistent stomach pain that may spread to your back, stop taking Mounjaro and seek immediate medical help. This could be pancreatitis.
Use NHS 111 for urgent advice. Call 999 if there is immediate danger, collapse, severe breathing difficulty or a severe allergic reaction.
Where To Read Next
Building new habits
How quieter appetite can become a chance to build habits that support long-term health.
Weight regain
What to know if you are worried about weight returning after stopping treatment.
Common side effects
A short guide to what is common, what helps and when to ask for advice.
Eating well
How to make every bite count when appetite is reduced.
Risks and benefits
A balanced guide to benefits, side effects, rare risks and informed choice.
Detailed side effect help
Practical tips for nausea, constipation, reflux, burps, dry mouth and more.
Dr Mel’s Notebook
Did you know?
Side effects often happen when starting or increasing the dose, and they often improve over time. Severe symptoms still need advice.
Try this today
Choose one habit you want to build while appetite feels quieter: a morning walk, protein at breakfast, more water, or eating more slowly.
The evidence
NICE recommends tirzepatide as an option for managing overweight and obesity in adults, and UK product information sets out dose, side effect and safety advice.
Key Messages
- Mounjaro can quieten appetite and food noise.
- Side effects are common, especially when starting or increasing the dose.
- The aim is not to eat as little as possible.
- Prioritise protein, fibre, fluids and small nourishing meals.
- Use the quieter appetite to build habits you want to keep.
- Severe pain, repeated vomiting, dehydration or allergic symptoms need urgent advice.
Useful Sources
Mounjaro KwikPen Patient Information Leaflet, emc
Mounjaro KwikPen Instructions for Use, emc
NICE TA1026: Tirzepatide for managing overweight and obesity
NICE: Prescribing, reviewing and stopping tirzepatide
MHRA: GLP-1 medicines—what you need to know
First published July 2026. Last reviewed: 15 July 2026. Planned review: October 2026, or earlier if MHRA/NICE/product information changes.
Prepared for the Pathfields Healthy Living Portal.