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Harley Weight Loss Clinic Library

Mounjaro

Mounjaro is a self-injectable treatment used to support weight loss. The active ingredient is tirzepatide, which can help regulate blood sugar levels to reduce cravings and lower your appetite.

  • Genuine UK medicine
  • Consult with UK GMC registered clinicians
  • Harley Street Specialist assessments

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What is Mounjaro?

Mounjaro is a treatment designed to help patients lose weight. It contains tirzepatide, which can help your body better manage its blood sugar levels. In conjunction with a supportive diet and exercise programme, this can help you lose weight.

Mounjaro is available in various doses, starting at 2.5 mg. Your prescribing doctor or clinician may advise adjusting your dose at certain intervals to enable your body to adjust to the medication.

Mounjaro is used to support weight loss and as a treatment for type 2 diabetes.

Tirzepatide — the active ingredient in Mounjaro — activates two hormonal receptors in the body: GLP-1 and GIP.

Activating the glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptors helps your body release more insulin, which regulates your blood sugar levels. It also slows down your body’s digestive processes, keeping you fuller for longer. These mechanisms send signals to your brain that you’re full, making you feel less hungry and reducing cravings.

Mounjaro may be suitable for patients who:

  • Have a BMI over 30 (obesity).
  • Have a BMI over 27 (overweight), and who are experiencing weight-related health conditions such as prediabetes, high blood pressure, or heart problems.
  • Have been diagnosed with type 2 diabetes.


All patients must undergo a clinical assessment to ensure their suitability before being prescribed Mounjaro.

Mounjaro and Zepbound are the same medication under two different names. Both are self-injectable weight loss support treatments that contain tirzepatide.

Mounjaro is the only version that is licensed in the UK. Zepbound is licensed in the US (alongside Mounjaro).

Mounjaro is a self-injectable treatment. You can inject it yourself or with the help of someone else. You should administer one injection at the same time every week.

If you’re prescribed Mounjaro, your doctor or clinician will help you understand how to inject it and provide you with full instructions.

Mounjaro is injected under the skin in the stomach, thigh, or upper arm. You’ll administer a single injection once a week at the dose prescribed by your clinician.

Your Mounjaro dosage will change over time so your body can adjust to the medication. Always make sure you’re using the right dosage at the right time, and check the needle isn’t bent or damaged in any way. It’s also important to check the medication isn’t frozen and doesn’t contain visible debris or particles before use.

Injecting Mounjaro may seem daunting at first, but your clinical team will support you to ensure you feel confident in the process.

If you’re injecting Mounjaro yourself, you should inject it in your stomach or thighs. If someone else is administering the treatment, they may inject the back of your upper arm. Don’t attempt to inject the back of your arm yourself.

It’s important to rotate the injection site each time. You should always inject at least an inch away from the previous injection site, and at least 5 cm away from the navel.

Mounjaro starts working immediately, though you won’t always feel the effects straight away. It may take a few weeks for you to feel a noticeable reduction in appetite and changes to your eating habits.

You should not use Mounjaro if:

  • You’re pregnant or breastfeeding;
  • You’re under 18;
  • You’re taking certain other medicines to manage diabetes;
  • You have certain digestive problems;
  • You have a history of pancreatitis or thyroid cancer;
  • You’re allergic to tirzepatide or any other ingredients in this treatment.

Mounjaro is a relatively new licensed treatment, which means it is being closely monitored for adverse reactions. If you experience any side effects while using Mounjaro, report them on a Yellow Card

All patients seeking weight loss treatment must disclose a full accurate medical history. Certain conditions or medications can make Mounjaro unsuitable for you, which is why it’s important to tell your prescribing clinician so they can ensure any prescribed treatments are safe for you to use.

Like all medicines, Mounjaro is known to cause some side effects. The most common side effects of Mounjaro include:

  • Nausea and vomiting
  • Diarrhoea
  • Constipation
  • Fatigue
  • Lightheadedness
  • Gastroesophageal reflux (GER) and heartburn
  • Low blood sugar
  • Hair loss
  • Redness and swelling at the injection site


Rare side effects can also occur. These include pancreatitis (inflammation of the pancreas) and anaphylaxis (extreme allergic reaction). If you have severe stomach pain, difficulty breathing, or swelling of the lips, face, or tongue, seek immediate medical attention.

Find out more about the potential side effects of Mounjaro in the Patient Information Leaflet

Most Mounjaro side effects are mild and manageable, and will disappear as your body adjusts to the treatment. Slowly increasing your Mounjaro dose (rather than starting with a higher dose) helps your body to acclimatise, reducing the risk and severity of side effects.

If using Mounjaro makes you feel unwell, there are ways to manage these side effects:

  • Inject yourself at the same time every week to ensure a regular interval between doses.
  • If you feel nauseous, sip water regularly and eat smaller meals more often.
  • Increase fibre in your diet to ensure regular bowel movements if you have constipation.
  • Exercise can help with constipation and fatigue, as well as contributing to a healthy lifestyle that supports your weight loss goals.

Changing your diet and increasing physical activity to ensure you use more calories than you eat can help with weight loss. Lifestyle changes are important even if you do use medical treatments, as these will help you maintain a healthy weight in the long-term.

Certain treatments may also help support your weight loss journey. These medicines work in a similar way, though they contain different active ingredients. Some weight loss treatments are available as tablets rather than injectable medications.

Any patient considering medical weight loss treatment should only do so under clinical supervision, and after a complete eligibility assessment.

Medically reviewed

Last reviewed on 31/12/2025

This content has been medically reviewed to ensure clinical accuracy, evidence-based guidance, and alignment with current best practice in metabolic, liver, and lifestyle medicine.

Approved by:

Dr. Saima Ajaz
BSc, MBBS, MPhil, PhD, Dip IBLM/BSLM, DABRM

Approved by:

Dr. Saima Ajaz
BSc, MBBS, MPhil, PhD, Dip IBLM/BSLM, DABRM

Dr Saima Ajaz is a specialist hepatologist and Lifestyle Medicine Physician at the Institute of Liver Studies, King’s College Hospital, and an Honorary Senior Clinical Lecturer at King’s College London. She brings over 20 years of clinical and research experience in metabolic health, fatty liver disease, and chronic metabolic disorders, integrating lifestyle, nutrition, and personalised medicine into patient-centred care.