Mounjaro (tirzepatide) is a weight loss injection that mimics natural hormones in your body. It works by reducing your appetite and making you feel fuller for longer. It is most effective when used alongside a low-calorie diet and an exercise plan for healthy weight loss.

How does Mounjaro work?

Mounjaro works by reducing your appetite, so you feel fuller after having a meal. This helps you lose weight by making it easier to avoid overeating and snacking, reducing the amount of calories you eat.

Mounjaro contains the active ingredient tirzepatide, which is a type of medication known as both a ‘GIP and GLP-1 agonist’. This means it mimics the effects of naturally occurring hormones that are responsible for regulating your appetite and the speed at which food moves through your intestines. It can also help to stabilise your blood sugar levels by increasing insulin production.

How long does it take for Mounjaro work?

Mounjaro starts to work by reducing your appetite, but you might not start to feel the effect straight away. From week 1 onwards, you should feel Mounjaro working, though the extent of this varies from person to person.

Mounjaro is most effective when you follow a healthy diet and exercise routine. You may find that you experience side effects between weeks 1 to 5 as your body adjusts to the medication. This may happen again during a dose increase but should get better over time.

Clinical studies show that patients can lose an average 22.5% of their starting weight after 72 weeks on higher doses, with strong results even at lower doses

What studies show:

Around 16% weight loss at lower doses
Around 21% at mid doses
An average 22.5% at the highest dose

Mounjaro dosage and routine

Mounjaro is available in 6 different strengths. When taking Mounjaro, you start on a low dose (2.5mg) which is gradually increased over time. This process helps your body get used to the medication and reduces the likelihood and severity of side effects.

Your doctor will guide you through the dosing schedule, which is designed to be increased every 4 weeks:

Weeks 1 to 4: Start with the 2.5 mg dose once weekly. This is a starter dose that helps your body get used to the medication.
Weeks 5 to 8: The dose is increased to 5 mg once weekly.
After week 8: Your doctor may increase the dose in 2.5 mg increments every 4 weeks if more weight control is needed. The available maintenance doses after the initial titration are 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg. The maximum dose is 15 mg once a week.

It is not always necessary to move up to the maximum dose. If you are getting good results and tolerating a lower dose like 5 mg or 7.5 mg, your doctor may recommend you stay on that dose. Never change your dose without consulting your doctor.

➤ You can find more information on our dedicated page explaining Mounjaro dosages.

Mounjaro prices

Dose	Price
Prices include treatment, consultation, 24/7 aftercare, weight loss pack, and support. If our services are not suitable, you will not be charged.
2.5mg	£169.99
5mg	£187.99
7.5mg	£249.99
10mg	£279.99
12.5mg	£299.99
15mg	£309.99

How to use Mounjaro

To use Mounjaro injections safely, you should:

take your current dose as instructed by your doctor – each Mounjaro pen contains 4 doses of the same strength (lasting 4 weeks)
only inject Mounjaro (tirzepatide) into your skin, never into a vein or muscle
inject Mounjaro once a week, at around the same time each week

Always follow your doctor’s instructions, and read through the patient information leaflet and user manual carefully before taking Mounjaro. Once you have chosen a day and time that suits you to inject Mounjaro, you can prepare to take it.

The main places to inject Mounjaro are the abdomen or upper legs. This image shows how to do that

Step 1: Preparation

Check the pen. Make sure it’s the correct medication and dose, is not expired, and is not damaged. The liquid inside should be clear and colourless to slightly yellow. Do not use it if it is cloudy, has particles, or is frozen.
Wash your hands thoroughly with soapy water.

Step 2: Attaching the needle

Take a new needle and pull off the paper tab.
Push the capped needle straight onto the pen and twist it clockwise until it is tight.
Pull off the outer needle cap (do not throw it away, you’ll need this later) and then pull off the inner needle cap (throw this one away).

Step 3: Priming the pen (new pens only)

You must prime every new pen before the first use. You do not need to prime it again before the other 3 doses in the same pen.

Turn the dose knob until you see the primed symbol, which looks like an extended line.
Press and hold the dose button until you see the ‘0’ icon in the dose window. You should see a small stream of liquid. This shows the pen is ready.

Step 4: Injecting the dose

Choose your injection site. You can inject into the skin of your abdomen (stomach area, at least 5cm from your belly button), the front of your thighs, or your upper arms. You should rotate your injection site each week.
Dial your dose. Turn the dose knob until it stops and you see the ‘1’ icon. This is your dose. Do not try to turn it further.
Inject the medication. Insert the needle into your skin at the chosen site. Press and hold the dose button. Keep it held down and watch the dose counter.
Hold for 6 seconds. Once the dose counter shows the ‘0’ icon, slowly count to 6 while still holding the button and keeping the needle in your skin. This ensures you get the full dose. Remove the needle from your skin.

If you do not see the ‘0’ icon: insert the needle back into your skin and finish the injection, do not redial the dose. If you are unsure how to proceed, speak to a doctor or pharmacist.

Step 5: After the injection

Carefully put the outer needle cap back onto the needle.
Unscrew the capped needle and dispose of it safely in a sharps bin.
Put the pen cap back on your Mounjaro pen and store it in the fridge or a cool dark place below 30°C.

Worried about injecting?

“We understand that it may sound off-putting to self-inject your medication. However, the Mounjaro KwikPen is designed in a way that is easy for you to use, even without a clinical professional present. Your Mounjaro pen uses a pre-filled injection with a smaller needle which is different to injections you might have at your GP practice (such as for a vaccine).” – Dr Zenon Andreou, Chief Medical Officer

If you request self-injection medication from ZAVA, our doctors will give you advice on how to take it and you can message them for free through your account if you need extra support.

What is the most effective way to inject Mounjaro?

No particular injection site will make the medication more effective. The most effective place to inject Mounjaro is the one that is most comfortable for you.

Can you stay on Mounjaro forever?

Mounjaro is considered a safe and effective long-term weight loss treatment. Trials have reported the treatment safe to be taken for as long as 88 weeks. Studies reported a significant decrease in risk factors for weight-related conditions such as high blood pressure and diabetes, and health benefits were reported with continued treatment with the maximum dose of tirzepatide.

However, it’s important to note as with any medication, side effects can happen at any time. Taking Mounjaro may increase the risk of digestive problems, and in some cases cause conditions such as pancreatitis. If you get any side effects when taking Mounjaro, you must let your doctor know and monitor them. If they get worse, tell your doctor straight away.

What happens when you stop taking Mounjaro?

When you stop taking Mounjaro, the amount of tirzepatide in your system will slowly drop to nothing. You will lose the blood sugar-regulating effect and your appetite will go back to normal. If you’re using Mounjaro for weight loss and stop, you may find that your weight goes back to how it was before you started your treatment if you do not continue with your weight loss plan.

The half-life of tirzepatide (Mounjaro) is around 5 to 7 days, if you stop using Mounjaro, tirzepatide should be gone from your body in about 30 days.

You need to keep to your healthy diet and exercise regime to make sure you don’t put weight back on. Weight loss requires a long-term commitment, even with medication.

What should I do if I miss a dose?

Forgetting a dose can happen. What you should do next depends on how long it’s been since your dose was due.

If it has been 4 days or fewer since your missed dose: Take your dose as soon as you remember. Then take your next dose on your regularly scheduled day.
If it has been more than 4 days since your missed dose: Skip the missed dose completely. Take your next dose on your regularly scheduled day. Do not take two doses at once to make up for a missed one.

If you are unsure what to do, contact your doctor or pharmacist for advice. You can also change the day of the week you inject if needed, as long as there are at least 3 days (72 hours) between your two doses.

If you have more than a 2-week gap between doses, you'll need to go back to the lowest Mounjaro dose (2.5mg) and work your way up again.

What is the maintenance dose of Mounjaro?

Once you have reached your goal weight, you can choose to manage your weight by continuing treatment with Mounjaro. If you choose to do this, your doctor will recommend a maintenance dosage that is safe for you, which can help you sustain your progress.

➤ For more information on Mounjaro dosages, see our guide.

Note: There is no particular correct maintenance dose for Mounjaro. Each person’s weight loss journey looks different – one person may find they experience side effects on the highest maintenance dose, whereas another could find it is the most effective. If you request maintenance with ZAVA, our doctors assess your medical history and how you have tolerated Mounjaro throughout your journey to help you find the right dose for you and your health.

Safety and side effects

Like all medications, Mounjaro can have some side effects. However, these will not affect everyone who uses Mounjaro, and your dose will be increased slowly to minimise your chances of getting them.

Very common Mounjaro side effects include:

nausea (feeling sick) and vomiting (being sick)
diarrhoea
constipation
low blood sugar (when used for the treatment of type 2 diabetes alongside sulphonylurea or insulin)
stomach pain

These side effects are not usually severe and tend to go away as your body adjusts to the medication.

Who should not take Mounjaro?

You should not take Mounjaro injections if you:

are under 18
are pregnant, trying to get pregnant, or breastfeeding
are allergic to any ingredients in the Mounjaro pen
do not meet the criteria for treatment
have not been approved for Mounjaro treatment by a doctor

Speak to your doctor before taking Mounjaro if you:

have severe problems with food digestion
have ever had pancreatitis
have problems with your eyes (either diabetic retinopathy or macular oedema)
are on diabetes medication

Is Mounjaro safe?

Mounjaro is a safe and effective weight loss treatment. It was approved for weight loss by the Medicines and Healthcare products Regulatory Agency (MHRA) in November 2023. This means that Mounjaro is officially safe to use for patients who are prescribed it by a registered health practitioner.

Studies report that it is common to experience side effects as your body adjusts to Mounjaro, particularly as your dosage is increased.

In most cases, common and mild side effects of Mounjaro can be managed at home and often go away in time.

Mounjaro warnings and risks

As Mounjaro can cause vomiting and diarrhoea, it can lead to dehydration if you do not get enough fluids. Make sure to drink plenty of water while taking Mounjaro and speak to your doctor if these side effects become severe. They may tell you to stop using Mounjaro or lower your dose.

Mounjaro can affect how well the contraceptive pill works. If you’re taking an oral contraceptive, such as the combined contraceptive pill or mini pill, you should:

use another method of contraception (like condoms) or switch to a non-oral contraceptive for 4 weeks after starting the Mounjaro pen
do the same for 4 weeks after each Mounjaro dose increase

Mounjaro and the morning after pill

Recommendation: Use the Copper Coil (IUD) as an emergency contraceptive when taking Mounjaro.

Morning after pills might not be effective if you are taking Mounjaro. This is because Mounjaro works by slowing stomach emptying, which can stop ingredients in pills like levonorgestrel or Levonelle from absorbing properly. It’s not known if it affects pills like ellaOne, but the copper coil is still recommended to reduce the risk of pregnancy.

If you are already taking Mounjaro, and are using a regular contraceptive pill, to be sure your contraceptive remains effective, we recommend using barrier contraception (condoms) for:

4 weeks after you start Mounjaro
4 weeks after each dose increase

If you are currently taking or thinking of taking Mounjaro, and you need emergency contraception, we recommend the copper coil (IUD), which is:

a small, t-shaped device inserted by a healthcare provider
highly effective, and you can insert it 120 hours (5 days) after unprotected sex (or ovulation)
accessible at some local GP surgeries or at sexual health clinics
can be kept in as regular contraception
not affected by Mounjaro

What medications does Mounjaro interact with?

Mounjaro weight loss injections can lower your blood sugar levels too much if taken for type 2 diabetes in combination with sulphonylurea, insulin, metformin, and sodium-glucose co-transporter 2 inhibitors (other diabetes treatments). Tell your doctor if you’re taking any of these medications, as they may need to adjust your dose.

You should not take Mounjaro alongside other weight loss injections, such as liraglutide or Wegovy. This could increase the risk of serious health risks and side effects.

For information on any other interactions with medications, including non-prescription and herbal remedies, speak to your doctor or check the patient information leaflet.

What foods should I avoid when taking Mounjaro?

As Mounjaro is either used for weight loss or regulating blood sugar levels, it should be taken alongside a healthy diet and exercise regime. You do not have to completely avoid any foods, but aim for a balanced diet.

Foods to cut back on when using Mounjaro include:

greasy or fried foods, especially if you get nausea or vomiting
high sugar foods, like chocolate or biscuits

It’s also good to avoid alcohol in large quantities as it lowers your blood sugar. This can increase the chances of having extremely low blood sugar if you are diabetic. Alcohol can also be high in calories and sugar and can lead to binge-eating.

➤ For more guidance on what to eat on Mounjaro, check out our in-house nutritionist reviewed Mounjaro diet plan.

Alternatives and comparisons

There are a range of alternatives to Mounjaro available at ZAVA for weight loss, including treatment both in the form of injection, and tablets. Remember that each weight loss treatment works differently for everybody.

Alternative weight loss injections

Alternative GLP-1 injections to Mounjaro (tirzepatide) include:

Wegovy

Wegovy is a once-weekly injection that contains the active ingredient semaglutide. It works in a similar way to Mounjaro by helping you lose weight through the way that it works to curb your cravings and suppress your appetite. Patients have been reported to lose an average 21% of their starting weight after 72 weeks when taking the 7.2mg dose.

If you think Wegovy may be a better alternative for you and you are currently taking Mounjaro, you can find more information on switching from Mounjaro to Wegovy in our article.

Nevolat

Nevolat is a once daily injection. It contains liraglutide, which is the same active ingredient that was in Saxenda which is now long-term out of stock. Patients lose up to 8% of their starting weight in just 56 weeks on the maintenance dose of 3.0mg of Nevolat.

If you are currently on your weight loss journey with us at ZAVA and are thinking of switching from Mounjaro, contact us on your patient account. One of our doctors will be able to assess whether it is right for you based on your current personal health and medical history.

Weight loss tablets

You may feel that Mounjaro, a weekly injection medication, is not suiting your lifestyle. There are several oral pill based weight loss treatment alternatives if you feel injections are not right for you and your weight loss journey.

Orlistat (120mg)

Orlistat is a weight loss tablet containing orlistat, it is taken three times a day at meal times. You must take the tablet with meals which contain fat because it works by reducing the amount of fat absorbed into your body. For best results, it should be taken alongside a low fat diet and regular exercise. Orlistat is available via prescription and is available in 120 mg at ZAVA.

Xenical (120mg)

Xenical is a branded version of the generic Orlistat, which means it works in the exact same way (to reduce the amount of fat your body absorbs), it just has a different name, price and packaging. It contains the active ingredient orlistat. Just like orlistat, you should take it three times a day with meals, and when taking Xenical you should follow a low fat, low calorie diet and a regular exercise routine for it to be effective. Xenical is available via prescription only and is available in 120 mg at ZAVA.

Alli (60mg)

Alli is an over-the-counter weight loss tablet, meaning it is available without a prescription. Like Xenical and Orlistat, it contains the active ingredient orlistat and therefore works in the same way to reduce the amount of fat that your body absorbs from meals. The tablets should only be taken up to three times per day at meal times, and the treatment is most effective when following a low-calorie, low-fat diet and regular exercise. Alli contains 60mg, which is less than the orlistat tablets like Orlistat and Xenical - on prescription Orlistat and Xenical contain 120mg. Studies have found that alli can help patients lose weight 50% faster than with dieting alone. Another study found 54.6% of patients lost at least 5% of their starting weight after 6 months of taking alli alongside a low-calorie and low-fat diet.

Mysimba

Mysimba is an oral tablet that you take once or twice a day depending on what your doctor prescribes. It contains the active ingredients naltrexone hydrochloride and bupropion hydrochloride which work on the areas of your brain responsible for food intake, hunger levels and energy. In turn, it helps you lose weight by reducing your appetite so that you feel fuller for longer. In clinical studies, patients treated with Mysimba lost an average 8.1% of their starting weight after 56 weeks of treatment.

Thinking of switching from Mounjaro to an alternative weight loss treatment? Start a consultation with us today, one of our doctors will be able to find a suitable treatment for you. If you are still deciding, browse our Weight Loss Treatment Service.

Frequently asked questions

How long does Mounjaro stay in your system?

Mounjaro has a half-life of 5 days. This is how long it takes for half the dose of tirzepatide to leave your system. After your last dose of Mounjaro, it should take around 25 days for all traces of it to leave your system.

Is Mounjaro a GLP-1 agonist?

Yes, Mounjaro is a GLP-1 receptor agonist, which means it acts like the hormone GLP-1 in your body. This is similar to other weight loss medications like Saxenda and Wegovy. However, unlike Saxenda and Wegovy, Mounjaro is also a GIP receptor agonist.

Can I take Mounjaro when I'm pregnant or breastfeeding?

No, Mounjaro isn’t safe for pregnancy or breastfeeding. There hasn’t been enough research into how this could affect the baby. If you are pregnant or breastfeeding and want weight loss treatment, talk to your GP.

How do I calculate my BMI?

Your body mass index (BMI) is a way to check your health based on your weight and height, and can let you know if you are underweight, healthy, or overweight. The way to calculate your BMI is your weight in kg divided by the square of your height in metres, or BMI = weight(kg)/height(m)2

If you know your weight and height, you can quickly and easily calculate your BMI with our BMI weight loss calculator.

What if I'm not losing weight on Mounjaro?

It can be discouraging if you’re not seeing the weight loss results you expected with Mounjaro. If you’re concerned, here are a few things to consider and steps you can take:

Be patient and manage expectations: It's normal to have weeks where you lose more, less, or no weight at all. Mounjaro works best over several months, alongside lifestyle changes, so you might not see drastic changes straight away. While you may notice that you are feeling less hungry, or even lose a little bit of weight, it usually takes up to 12 weeks until you see significant weight loss.
Review your diet: Mounjaro can help you maintain a low calorie diet, but it is not a replacement for one. You still need to make healthy eating choices that keep you in a calorie deficit so you lose weight. A balanced diet rich in protein, fibre, and healthy fats can help with feeling full, and keeping a food diary can help identify areas for improvement.
Stay hydrated: Staying hydrated can boost your metabolism and help you feel full. Sometimes your body can mistake thirst for hunger, which can lead to snacking. If you're hydrated you can also reduce the chance of getting side effects.
Assess your physical activity: Regular exercise can help you maximise your weight loss and improve your overall health. It helps to burn calories and build muscle (which boosts metabolism). Even a 15 minute walk every day goes a long way to help you lose weight.
Check your dose: You start on a low dose of Mounjaro and gradually increase. The lower doses are to help your body get used to the medication, but you may not see as much weight loss as on the higher doses. If you have been on the same dose for a while and your weight loss has stalled, you should speak to your doctor about increasing your dose.
Get enough sleep: If you’re not getting enough sleep, you might also notice a change on the scales. This is because a lack of sleep can affect your hormones , brain function, energy levels, and other factors, which can contribute to weight gain.
Speak to your doctor: If you have followed these steps and are still not losing weight on Mounjaro, it’s important to talk to your doctor. They can assess your progress, see if there are any medical issues stopping your weight loss, and determine whether Mounjaro is the right treatment for you. You may see better results on an alternative treatment, such as Wegovy.

Can emergency contraception still work if I’m taking Mounjaro?

Likely not. Mounjaro (tirzepatide) can stop emergency contraceptive pills that you take by mouth from working properly, which means you could still get pregnant. This is because Mounjaro can reduce the absorption of the ingredients in morning after pills as it slows down stomach emptying.

For those starting or using Mounjaro, we recommend the copper coil. It can be inserted up to 5 days after unprotected sex and then used as a regular contraceptive method, and its effectiveness is not affected by Mounjaro.

Does Mounjaro work like insulin?

Mounjaro (tirzepatide) is not an insulin, although it can help your body to produce more of it. Mounjaro contains tirzepatide, which should not be injected at the same time as insulin. If you have type 2 diabetes, you will need to have your doctor create a tailored treatment plan for you.

When was Mounjaro approved for weight loss?

Mounjaro became licensed and approved for weight loss in the UK in November 2023, Mounjaro has been approved for weight loss if you have:

a BMI (body mass index) of 30 kg/m² or higher (obesity)
a BMI between 27 and 30 kg/m² (overweight) and a weight-related health condition, such as high cholesterol, high blood pressure, prediabetes, or heart problems

Sources

Mounjaro KwikPen 2.5/5/7.5/10/12.5/15 mg solution for injection in pre-filled pen, emc [accessed 05 February 2026]

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How to use Mounjaro, Mounjaro [accessed 05 February 2026]

Obesity, NHS [accessed 05 February 2026]

Tirzepatide for treating type 2 diabetes, NICE [accessed 05 February 2026]

Tirzepatide Once Weekly for the Treatment of Obesity, The New England Journal of Medicine [accessed 05 February 2026]

Continued Treatment With Tirzepatide for Maintenance of Weight reduction in Adults With Obesity, Journal of the American Medical Association [accessed 05 February 2026]

Weight management injections, NHS England [accessed 05 February 2026]

NICE describes how weight loss drug tirzepatide will be rolled out, NICE [accessed 05 February 2026]

Once-Weekly Semaglutide in Adults with Overweight or Obesity, NEJM [accessed 05 February 2026]

FSRH Statement: Glucagon-like peptide-1 (GLP-1) agonists and oral contraception, The Faculty of Sexual & Reproductive Healthcare [accessed 05 February 2026]

Delivery

How ZAVA can help you lose weight with Mounjaro

13kg

Lost over 4 months

“I can now play with the children better and pick them up and things like that. My mobility has improved enormously. I am much less restricted and, above all, much less exhausted. And the clothes that were at the back of the closet fit again!” — Anika

Mounjaro injectable pen

What is Mounjaro?