The usual starting dose of Mounjaro for adults is 2.5mg once weekly. Your prescriber will decide whether Mounjaro is suitable for you based on your medical history and individual clinical assessment.
Once you start treatment, you may have practical questions that are not always covered by a simple dosing schedule. What happens if you miss a dose? Can you take Mounjaro at a different time? When can your dose increase? What should you do if you are travelling or storing your pen?
If you have been prescribed Mounjaro, or you are considering it for weight management or type 2 diabetes, this guide explains the basics in straightforward language. It covers the starting dose, how the dose may change, how to use your pen, what to do if you miss a dose, and practical points about storage, side effects and contraception.
The most important point is to use Mounjaro exactly as prescribed. Do not change your dose, take extra doses or combine pens without speaking to your prescriber.
The information below is based on the UK patient information leaflet supplied with Mounjaro. Always read the leaflet that comes with your medicine, as it provides the most specific instructions for your treatment and pen.
The Basics
| Question | Answer |
|---|---|
| How often is Mounjaro taken? | Once a week |
| Does it need to be at a set time of day? | No. Any time, with or without food |
| Should it be the same day each week? | Yes, where possible |
| How many doses are in a pen? | Four |
| How long does one pen last? | Four weeks |
| How is it given? | Subcutaneous injection into the abdomen, thigh, or back of the upper arm |
The Mounjaro pen is not single use
This is an easy point to miss, and it can lead to unnecessary waste.
The Mounjaro KwikPen is a multi dose, single patient use pen designed to deliver four weekly doses. You use it once a week for four weeks and then discard it. A small amount of medicine may remain in the pen after the fourth dose. This is expected and should not be treated as an extra dose. Do not try to use the remaining medicine.
The pen should also be discarded 30 days after first use, whichever comes first.
If you are unsure how to use your pen, speak to your pharmacy team or prescriber and check the Instructions for Use supplied with your medicine. You should also check the pen label and packaging for the expiry date before use.
Which Starting Dose or Strength Do You Start On?
Mounjaro is available in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.
The usual Mounjaro starting dose for adults is 2.5mg once weekly for four weeks. If appropriate, your prescriber may then increase the dose to 5mg once weekly. Further increases may be considered at intervals of at least four weeks, depending on your response and how well you tolerate treatment.
A Mounjaro dosage chart or simple dosage chart can help you understand the usual dosing schedule, but it should not be used to decide your own dose.
Your prescriber decides where you start and whether your dose should change. They will consider your medical history, how you respond to treatment, side effects and other relevant clinical factors. Your weight loss goals and progress may also form part of the wider treatment discussion.
The dose is not something you should choose based on price or information on a website. The highest licensed dose is 15mg once weekly.
Can you start at 5mg?
The usual licensed starting dose is 2.5mg once weekly, so you should not decide to start at 5mg yourself.
The dosing schedule begins with a lower dose and may then increase gradually. This allows your prescriber to assess how you respond to treatment and how well you tolerate each strength.
If you have previously taken tirzepatide or are moving from another provider, tell your prescriber which strength you used, how long you used it and when you last took it. This information can help them assess the most appropriate treatment plan for you.
Timing Questions
Can you take Mounjaro a day early?
If you need to change your usual injection day, you can change it as long as at least three days have passed since your last injection.
Once you have chosen a new injection day, continue taking your weekly dose on that day.
The three day interval is the minimum gap when changing your injection day. It does not mean that you should take Mounjaro every three days or change your schedule regularly without discussing it with your prescriber.
Can you take Mounjaro every five days?
No. Mounjaro is intended to be taken once weekly, and taking it every five days is not the recommended dosing schedule.
Taking doses more frequently than prescribed could increase your exposure to the medicine and may increase the risk of side effects. If you feel your current dose is not working well or you are having problems with treatment, speak to your prescriber rather than changing the schedule yourself.
Can you take Mounjaro every other week, or every two weeks?
No. Mounjaro is designed to be taken once weekly, and taking it every two weeks is not the recommended dosing schedule.
If you are thinking about spacing doses because of cost or side effects, talk to your prescriber first. They can discuss whether your current treatment remains appropriate and what options may be available. If cost is a concern, you can also ask whether you may be eligible for NHS treatment.
What if you miss a dose?
If you remember a missed dose within four days, take it as soon as possible. If more than four days have passed, skip the missed dose and take your next dose on your usual scheduled day.
Do not take a double dose to make up for a missed dose.
If you are unsure when to take your next dose, particularly if you have missed more than one dose, speak to your prescriber or pharmacy team before taking another dose.
Can You Combine Two Pens to Make a Higher Dose?
No. Do not use two pens to make up a higher prescribed dose.
For example, two 2.5mg injections should not be used as a substitute for a prescribed 5mg dose. If you are unsure about your prescribed strength, speak to your prescriber or pharmacy team before taking another dose. Using more than one injection can also increase the chance of a dosing error or injection site reactions.
If you have run out of your prescribed strength, your pen is damaged, or you think you have received the wrong medicine or strength, contact your pharmacy for advice. Do not try to adjust the dose yourself.
If you think you have taken more Mounjaro than prescribed, contact your prescriber or NHS 111 for advice. Taking more than the prescribed amount may increase the risk of side effects, so seek medical advice promptly if this happens.
What to Expect Around Your First Injection and Injection Sites
Before your first injection, read the Instructions for Use supplied with your Mounjaro pen. It explains how to prepare the pen, set the dose and give the injection. If anything is unclear, ask your prescriber or pharmacy team for help.
Injection sites. Mounjaro can be injected into the abdomen, thigh or back of the upper arm. You can use the same general area each week, but choose a different spot within that area to help reduce irritation. If you want to inject into the back of your upper arm, ask someone else to help you.
Side effects. Common side effects include nausea, diarrhoea, vomiting, constipation, indigestion and reduced appetite. These may be more noticeable when you first start treatment or after a dose increase, and they may become less noticeable as treatment continues. Individual experiences vary. Eating smaller portions, stopping when you feel full and drinking enough fluids may help with some digestive symptoms.
Less common but more serious risks include pancreatitis, gallbladder problems and dehydration that may affect kidney function. Low blood sugar can also occur, particularly in people who take Mounjaro with insulin or a sulfonylurea.
Contact your prescriber, GP or NHS 111 if your side effects are severe, persistent or worrying, or if you develop severe abdominal pain, particularly pain that spreads to the back, persistent vomiting, signs of dehydration or symptoms of low blood sugar. Seek urgent medical help if you develop signs of a serious allergic reaction. Suspected side effects can also be reported through the MHRA Yellow Card scheme.
Contraception
If you use the oral contraceptive pill, discuss this with your prescriber before starting or increasing tirzepatide.
MHRA advice issued in June 2025 recommends using additional or non oral contraception for four weeks after starting tirzepatide and for four weeks after each increase in strength. This is because tirzepatide can delay gastric emptying, which may affect the absorption of oral contraceptives.
This advice can apply again whenever your dose is increased, so mention your contraception during your consultation if it is relevant to you.
Storage
- Store unopened Mounjaro pens in a refrigerator between 2°C and 8°C
- A pen that is in use may be kept at room temperature, up to 30°C, for the period specified in the patient information leaflet
- Do not freeze a pen. Do not use it if it has been frozen
- Keep pens in the original carton and protect them from light and heat
- Discard the pen after four doses or 30 days after first use, as instructed for your pen
- Used needles should be placed in a sharps bin and not in household waste
- Keep Mounjaro pens and needles out of the sight and reach of children
What Mounjaro Is and How It Works
Mounjaro is the brand name for tirzepatide, made by Eli Lilly. In the UK, it is licensed for weight management alongside a reduced calorie diet and increased physical activity. It is also licensed separately for the treatment of type 2 diabetes.
Tirzepatide works by activating two gut hormone receptors called GIP and GLP 1. Unlike semaglutide, which acts on the GLP 1 receptor, tirzepatide acts on both. These hormones are involved in appetite regulation, feelings of fullness and blood glucose control. Tirzepatide also slows gastric emptying, particularly after a dose.
Mounjaro is intended to be used alongside dietary and lifestyle changes rather than as a replacement for them. In the SURMOUNT 1 clinical trial, the highest dose was associated with a mean weight reduction of around 20 per cent over 72 weeks. This was an average result across the study group, so it should not be taken as a prediction of how much weight any individual will lose. Responses can vary depending on factors such as starting weight, treatment duration, dose and individual response.
NICE technology appraisal TA1026 also includes a review point. If less than 5 per cent of initial body weight has been lost after six months on the highest tolerated dose, the clinician should decide whether continuing treatment is appropriate. If treatment continues, your prescriber will review your response and tolerability and determine the most appropriate dose for you.
Who It Is Licensed For
For weight management, Mounjaro is licensed for adults with a BMI of 30 or above, or a BMI of 27 or above where a weight related health condition is present. Examples include hypertension, dyslipidaemia, obstructive sleep apnoea, cardiovascular disease, prediabetes and type 2 diabetes.
Mounjaro may not be suitable for everyone. Tell your prescriber if you are pregnant, breastfeeding or trying to conceive, have a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2, have had pancreatitis, have certain digestive conditions, or are under 18.
These criteria are a general guide and are not a substitute for a clinical assessment. Your prescriber will consider your medical history, current medicines and individual circumstances before deciding whether Mounjaro is appropriate for you. Treatment can also be reviewed during treatment if your circumstances change.
Our guide to prescription weight loss treatments covers other available options. Current pricing is available on the Mounjaro treatment page. Mounjaro is only supplied following an appropriate clinical assessment and prescribing decision.
Key Takeaways
- Mounjaro is taken once a week, at any time of day, with or without food
- Each KwikPen contains four weekly doses and is discarded after the fourth dose
- The pen is designed for multiple doses from the same pen, not for single use
- If you need to change your injection day, make sure at least three days have passed since your previous injection
- If you are more than four days late with a dose, follow the missed dose instructions in your patient information leaflet and do not take a double dose
- Never combine two pens to make up a higher dose
- Your prescriber decides your strength based on your clinical assessment, response and tolerability
- Your patient information leaflet is the most specific source of instructions for your medicine, so read it carefully before use