Mounjaro® for Weight Loss: How It Works, Side Effects & More
Trying to lose weight can be challenging. Weight loss medicine — like Mounjaro® (tirzepatide) — can make it a bit easier. But how does Mounjaro® work?
Mounjaro® is a prescription weight loss injection. When used with a reduced-calorie diet and increased physical activity, Mounjaro® can help you lose a significant amount of weight.
In the United Kingdom, the Medicines and Healthcare products Regulatory Agency (MHRA) has authorised Mounjaro® for weight management. Although it‘s available through the NHS (National Health Service), the criteria are strict, and not all regions have access to the medication. For that reason, private prescriptions are currently the most common route.
Here‘s everything you need to know about Mounjaro®, including how it works, Mounjaro® dosage, Mounjaro® weight loss side effects, and Mounjaro® results you can expect.
What Is Mounjaro®?
Mounjaro® is a once‑weekly injection containing tirzepatide. It‘s licensed in the UK for weight management and also treats type 2 diabetes. Another U.S.‑only brand, Zepbound®, contains the same active ingredient but is not licensed in the UK.
This medication is manufactured by Eli Lilly, a pharmaceutical company. It‘s only available with a prescription.
Research shows Mounjaro® is highly effective in the treatment of obesity. In large clinical trials, weekly tirzepatide doses from 5 to 15mg (milligrams) helped adults without diabetes lose an average of 16 to 22 percent of their starting body weight. Adults with type 2 diabetes lost roughly 15 percent of their body weight when combining the medicine with lifestyle support.
Weight loss your way
Is Mounjaro® Licensed for Weight Loss in the UK?
Yes. In November 2023, the MHRA authorised Mounjaro® for weight management and weight loss in adults.
It‘s available both privately and via the NHS. However, most people in the UK go the private route for these reasons:
NHS access is limited by the criteria set out by the National Institute for Health and Care Excellence (NICE), which means not everybody qualifies for Mounjaro® through the National Health Service.
Mounjaro® isn‘t yet available in all regions in the UK.
Long waiting times mean it‘s more convenient to opt for private care.
In the UK, prescribing medicine for a purpose outside what it’s licensed for is called off‑license. Since Mounjaro® is now licensed for weight loss, weight loss use is on‑license. By contrast, Ozempic® (semaglutide) is licensed for diabetes only and its off‑license use for weight management is discouraged.
Who Is Mounjaro® Prescribed For?
Mounjaro® is prescribed for weight management in adults. However, it‘s typically only suggested for people who have a high body mass index (BMI).
Most private providers follow the MHRA‘s guidelines for prescribing Mounjaro®:
Adults with a BMI of at least 30 kg/m² (that‘s body weight in kilograms divided by height in meters squared)
Adults with a BMI of at least 27 kg/m² who also have a weight‑related health condition, such as high blood pressure (hypertension), high cholesterol, cardiovascular disease, or sleep apnoea
For ethnic groups at a higher metabolic risk (Chinese, South Asian, other Asian, Middle Eastern, Black African, and African‑Caribbean), clinicians may allow a lower BMI range (at least 25 kg/m²).
Meeting these BMI criteria won‘t make you a good candidate for Mounjaro® for certain, though.
You may be at risk of serious side effects of Mounjaro® if you:
Have a family history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN2)
Have had a severe allergic reaction to tirzepatide or any of the inactive substances in Mounjaro®
Are pregnant, breastfeeding, or planning to become pregnant soon
Have a disease of the liver, kidneys, or pancreas
To find out if Mounjaro® is suitable for you, speak with a clinician. Be sure to explain your health history, including your family‘s medical history and any previous weight loss attempts.
Some people also explore how tirzepatide may support weight management in specific conditions, such as Mounjaro® and PCOS.
How Does Mounjaro® Work?
Mounjaro® is a dual GIP/GLP‑1 receptor agonist. This means it activates receptors for two gut hormones: glucose‑dependent insulinotropic polypeptide (GIP) and glucagon‑like peptide‑1 (GLP‑1).
How does Mounjaro® work to support weight loss? By mimicking GLP-1 and GIP, tirzepatide aids weight loss by:
Reducing appetite and cravings for food
Increasing satiety (a feeling of fullness)
Slowing gastric emptying (how quickly digested food leaves the stomach), so meals keep you satisfied for longer
Supporting insulin release when glucose is high and inhibiting glucagon
These effects make it easier to maintain a calorie deficit (consuming fewer kcals than you expend each day) without constant hunger or cravings.
A 2023 systematic review looked at 10 clinical trials, which included a total of almost 10,000 participants. It concluded that tirzepatide was more effective than other medicines in reducing body weight, including other GLP-1 receptor agonists.
It‘s important to note that weight loss medications work best when combined with healthy lifestyle changes — think increased physical activity, a healthy diet, and stress management.
What‘s the Usual Mounjaro® Dosage for Weight Loss?
Typically, you‘ll start on a lower dose of Mounjaro® and gradually increase it over time.
Your treatment plan will usually go something like this:
A healthcare provider will prescribe a starting dose of 2.5mg per week.
After four weeks, you‘ll increase to a 5mg weekly dose.
If needed, your dose could increase in 2.5mg increments, up to a maximum dose of 15mg. You‘ll spend four weeks on each dose before increasing it again.
Once you reach your weight loss goals, you‘ll move to a maintenance dose.
Higher doses of Mounjaro® seem to be more effective for weight loss, but they carry the risk of worse side effects.
A 2022 study sponsored by Eli Lilly looked at the effects of tirzepatide at different doses. Participants took a once-weekly injection of 5mg, 10mg, or 15mg of tirzepatide or a placebo for 72 weeks. That included 20 weeks to increase the dose slowly.
At the end of the experiment, the average percentage change in weight was:
15 percent for those taking 5mg of tirzepatide
19.5 percent for those taking 10mg of tirzepatide
20.9 percent for those taking 15mg of tirzepatide
3.1 percent for those on the placebo
So, you might lose more weight on a higher dose — but it may also be difficult to tolerate the side effects. A prescribing clinician can work with you to find your best Mounjaro® dose for weight loss and tell you when to increase your dose.
What Are the Side Effects of Mounjaro®?
The most common side effects of Mounjaro® include:
Nausea or vomiting
Diarrhoea or constipation
Indigestion, bloating, or gastric reflux (heartburn)
Headache, fatigue, or dizziness
Decreased appetite
Irritation or bruising at the injection site
The gastric side effects of tirzepatide may be dose-dependent. This means higher doses come with a higher risk of some side effects.
Most of these side effects are worse when you start Mounjaro® or increase your dose. They typically go away after a few days or weeks.
Taking non-prescription anti-nausea medications, eating smaller meals, and sipping water throughout the day can help with some of the gastric side effects of GLP-1 medications. You may find it useful to review what to eat on Mounjaro® to help minimise stomach-related side effects.
Serious Mounjaro® Side Effects
Mounjaro® is associated with some rarer, but more serious side effects. While these are uncommon, you should be aware of the risks.
Potential serious side effects of Mounjaro® include:
Pancreatitis (inflammation of the pancreas)
Gallbladder disease
Kidney disease
Hypoglycemia (low blood sugar), particularly when combined with insulin or other GLP-1 medications
Allergic reactions
Acute kidney injury
Worsening diabetic retinopathy (for those with diabetes)
Severe gastrointestinal disease
In some studies, Mounjaro® caused thyroid C-cell tumours in rats. Although this hasn‘t been confirmed in humans, you should avoid tirzepatide if you or any close relatives have had medullary thyroid cancer or MEN2.
If you experience adverse events on Mounjaro®, seek urgent care. Be sure to report them via the MHRA Yellow Card scheme.
Mounjaro® How to Use
Mounjaro® is an injectable medication that comes in a pre-filled pen. You‘ll need to inject it once a week, according to the dosing schedule prescribed by your clinician.
How to Use Mounjaro® and Where to Inject Mounjaro®
Your clinician will give you specific instructions on your dosage, plus how to inject Mounjaro®. But here’s how it usually goes:
Inject yourself in the abdomen, thigh, or upper arm. Rotate sites each week to avoid irritation and bruising.
Before injecting, clean the area with an alcohol swab and let it dry.
Insert the pre-filled pen against the skin at a 90-degree angle. Press the pen and keep it in place for about 10 seconds so the full dose is delivered.
Place used needles or empty pens in a sharps bin. Many councils offer sharps collection or chemist drop‑off — check your local service.
For safety and optimal results, stick to the exact dosage prescribed by your clinician. If you have questions about safety, you can also read more about whether Mounjaro® is safe and how clinicians assess its risks and benefits.
When to Inject Mounjaro®
It’s best to pick a weekly “dose day“ you can stick to (e.g., Sunday evening or Monday morning) and set a phone reminder so you don’t miss a dose.
There‘s no best time of day to take Mounjaro®. Some prefer taking it in the evening, while others prefer the mornings. Generally, it‘s a good idea to take it around the same time every week.
How to Manage the Side Effects of Mounjaro®
Many people experience side effects after their first injection or after increasing their dose.
Here are some tips for managing those symptoms:
Eat light before your injection — smaller, lower‑fat meals — to reduce nausea.
Hydrate by drinking a glass of water 15 to 30 minutes before and after the shot.
Don‘t massage the site afterwards. If it‘s sore, a cool compress can ease tenderness.
If you feel queasy, sip water, ginger, or peppermint tea, or get some fresh air.
Non-prescription medication, like anti-nausea or anti-vomiting medicines, could help.
If you‘re experiencing severe side effects, seek urgent care. If your side effects aren’t dangerous but quite severe — e.g., significant nausea — discuss your dosage with your clinician.
What to Do If You Miss a Dose of Mounjaro®
First, don‘t fret! Just administer the injection as soon as you remember, as long as it‘s within four days of your usual injection day.
If it‘s been more than four days, simply skip the missed dose and take your next dose on your usual injection day.
Try not to miss your dose too often, as this can affect your weight loss results.
Mounjaro® Storage and Travel
Keep unused pens refrigerated (2 to 8°C). Once in use, most pens can be kept at room temperature for a limited time — check your leaflet. And don‘t freeze the medicine.
When travelling, use a cool bag or ice pack, keep pens in hand luggage, and carry a copy of your prescription for airport security — just in case.
Maximising Your Weight Loss Results on Mounjaro®
If you take Mounjaro®, you should also prioritise healthy lifestyle changes. This will help you reach your weight loss goals.
Try the following:
A reduced-calorie diet that focuses on whole foods
Ensuring you get enough protein and a variety of fruits and vegetables
A balanced training program (and increased movement in general)
Practising basic self-care — get enough sleep, stay hydrated, and manage stress
Your prescribing clinician can give you more advice on creating healthy lifestyle habits.
How to Get Mounjaro® for Weight Loss in the UK
You can get Mounjaro® through the NHS or privately. Getting Mounjaro® through the NHS can be challenging due to strict criteria for access, limited supply, and long waiting lists.
How to Get Mounjaro® Through the NHS
The NHS criteria for Mounjaro® are as follows:
Aged 18 or over
BMI of at least 35 (or at least 32.5 for certain minority ethnic groups)
At least one weight-related health condition
Enrolled in a specialist NHS weight management service (tier 3)
Here‘s how to access Mounjaro® through the NHS:
First, you‘ll need to make an appointment with a GP (general practitioner). They‘ll offer you a medical assessment and lifestyle advice.
If you meet NICE‘s criteria, the GP might refer you to a tier‑3 weight management service.
Tier-3 services include multidisciplinary support. You‘ll likely see a dietitian and therapist to support your weight loss plan.
After 12 weeks, if you haven‘t lost enough body weight, you might be offered Mounjaro® or another weight loss treatment.
Since these services often have strict criteria, long waiting times, and limited availability, many people opt for private treatment.
How to Get Mounjaro® Privately in the UK
The private prescription criteria for Mounjaro® are:
Aged 18 or over
BMI of at least 30 (or at least 27 with a weight-related health condition like sleep apnoea or high blood pressure)
If you meet these criteria, you can access Mounjaro® privately — including through online platforms like Hers UK.
Here‘s how the Hers process works:
Fill out a quick online assessment covering your BMI, medical history, and weight loss goals.
A UK-licensed care professional will review your answers and contact you about the next steps.
You‘ll receive a personalised plan with Mounjaro® (if appropriate), as well as guidance on exercise and diet
Your Mounjaro® injection pen will be delivered discreetly and quickly to your home.
If necessary, you can make a follow-up appointment with your care team to discuss issues, concerns, and side effects.
While getting tirzepatide privately will cost more than prescriptions through the NHS, it can be more convenient and faster.
What‘s the Cost of Mounjaro® in the UK?
Private prices for Mounjaro® vary by dose strength and provider care plan (consults, delivery, follow‑ups, etc.). In 2025, typical monthly ranges are roughly £129 to £249.
Remember, these prices are subject to change. With Hers UK, you‘ll see live pricing during the assessment.
How Long Does Mounjaro® Take to Work?
So, you‘ve got your shot — but how quickly does Mounjaro® work?
You‘ll often feel a difference before you see one. Tirzepatide reaches peak levels within one to three days of an injection, so many people notice less hunger and earlier fullness in the first week.
If you pair your injection with a healthy diet and increased movement, you can expect to lose a bit of weight within the first two to four weeks on the shot.
Your weight loss results will depend on factors like:
Your Mounjaro® dosage
Whether you miss any doses
Your unique biology
In most clinical studies, people lose 10 to 15 percent of their starting weight by week 24, while trials report 16 to 22 percent average loss depending on Mounjaro® dose (5 to 15mg) when paired with diet changes and physical activity.
If you’re curious about typical early progress, our guide on Mounjaro® weight loss by week breaks down what people often notice throughout treatment.
Unlock your treatment plan
What Happens When You Stop Taking Mounjaro®?
Once you reach your weight loss goals, you can move to a maintenance dose of Mounjaro®.
If you stop taking Mounjaro®, your appetite might return. If you end up eating more calories, you may put on weight.
Current evidence suggests structured maintenance plans (nutrition, activity, and behaviour changes) reduce the risk of regaining weight after stopping a weight loss medicine.
Alternatives to Mounjaro® in the UK
Mounjaro® is just one of many weight loss medicines. If tirzepatide isn’t suitable for you, a clinician might suggest another treatment.
Other weight loss medications include:
Wegovy® (semaglutide), a once-weekly GLP-1 injection
Saxenda® (liraglutide), a daily GLP-1 injection
Xenical® (orlistat), an oral med that partially blocks fat absorption
A healthcare professional can go over the benefits, drawbacks, side effects, and risks of each option and match you to the safest, most effective treatment.
All weight loss medications need to be paired with a healthy lifestyle to increase your chances of meeting your goals. This includes healthy eating habits, increased movement, and taking care of yourself.
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Final Thoughts on Mounjaro® for Weight Loss
Mounjaro® is a powerful weight loss medication. When paired with a balanced diet and physical activity, it can help you lose significant amounts of weight.
Remember this when considering Mounjaro®:
It works by mimicking two appetite-regulating hormones, GLP-1 and GIP. This helps you feel fuller for longer, which makes it easier to eat a reduced-calorie diet and lose weight.
It‘s available via the NHS and private clinics. However, access to Mounjaro® through the NHS is very limited, and waiting times can be long.
In the UK, you can get Mounjaro® through private online clinics like Hers. This can offer a convenient, simple way to access weight loss drugs.
Curious about whether you‘re eligible for Mounjaro®? Start a free Hers UK assessment to explore clinically proven weight loss medications.
This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your GP about the risks and benefits of any treatment.