The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Mounjaro for Medical Weight Management in the UK
Mounjaro is a prescription-only injection containing tirzepatide, licensed in the UK for medical weight management in adults. It works by activating two natural hormone pathways — GIP and GLP-1 — to help reduce appetite and support weight loss alongside diet and exercise. This dual mechanism is what distinguishes it from other weight loss injections like Wegovy (semaglutide), which targets only the GLP-1 pathway. If you're considering Mounjaro or want to understand how it fits into a medical weight management plan, this guide covers eligibility, how it works, dosing, and what to expect.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How Mounjaro Works as a Medical Treatment
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways in your body that regulate appetite and energy balance. GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) are hormones your gut naturally produces after eating. By mimicking and amplifying these signals, Mounjaro helps you feel fuller after smaller meals, reduces cravings, and may support your body's use of fat for energy.
Clinical trials showed that at the maximum dose (15 mg weekly), Mounjaro helped participants lose an average of approximately 20.9% of their body weight over 72 weeks — though individual results vary significantly. This effect is achieved when Mounjaro is used alongside a reduced-calorie diet and increased physical activity, not as a standalone treatment.
Mounjaro is available as a KwikPen pre-filled injection device administered once weekly, making it convenient for medical management. You can inject it into your stomach, upper thigh, or upper arm.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
UK Medical Eligibility and Access Routes
In the UK, Mounjaro may be prescribed for adults with a BMI of 30 or above, or BMI of 27–29.9 with at least one weight-related health condition (such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease). For people of South Asian, Chinese, Black African, or Black Caribbean backgrounds, the NHS recommends lower thresholds due to higher health risks at lower BMI levels.
Access is available through NHS specialist tier 3/4 weight management services (typically via GP referral, though availability and waiting times vary significantly by region) or through private prescribing following an online clinical assessment with a UK-licensed prescriber. Use our free BMI calculator to check where you fall, and try our GLP-1 weight loss calculator to see potential outcomes at different doses.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is Mounjaro the same as Ozempic?
No. Both contain semaglutide (in Ozempic's case) or tirzepatide (Mounjaro), but they are different medications with different mechanisms. Mounjaro contains tirzepatide and activates both GIP and GLP-1 pathways. It is specifically licensed for weight management in the UK. Always ensure your prescriber is issuing the correct medication for your needs.
What dose of Mounjaro should I start on?
The standard starting dose is 2.5 mg once weekly. Your prescriber will increase this gradually — typically by 2.5 mg every 4 weeks — up to a maximum of 15 mg weekly. The dose increase depends on how well you tolerate the medication and your response to treatment. Never adjust your dose without guidance from your prescriber.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro (tirzepatide) has been approved by NICE for use within NHS specialist weight management services. However, access is through tier 3/4 specialist services, not standard GP prescription. Availability and waiting times vary significantly by region and ICB. Your GP can refer you, but waiting lists can be lengthy in many areas.
How long does it take to see weight loss results with Mounjaro?
Most people begin to notice changes after 4–8 weeks of treatment, but the most significant results typically appear over 12–16 weeks. Weight loss continues to accumulate with ongoing treatment and dose increases. Remember that results vary — some people lose more weight than others, and weight loss depends on adhering to diet and exercise changes alongside the medication.
What are the most common side effects of Mounjaro?
The most common side effects are nausea, diarrhoea, vomiting, and constipation — particularly when starting or increasing doses. These often reduce over time. Other common side effects include stomach pain, indigestion, and injection site reactions. If you experience severe stomach pain, seek medical attention immediately as it could indicate pancreatitis. ```
Ready to take control of your weight loss journey?
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