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
Free tracker included with every download this week
How Mounjaro Supports Weight Loss in the UK
Mounjaro (tirzepatide) is a prescription-only weekly injection licensed in the UK for weight management in adults. It works by activating two natural hormone pathways—GIP and GLP-1—to help regulate appetite and support feeling fuller after meals. Clinical trials showed that people taking Mounjaro alongside a reduced-calorie diet and increased physical activity lost an average of 15–21% of their body weight over 72 weeks. However, individual results vary significantly, and Mounjaro is not suitable for everyone. This guide explains how it works, who may be eligible, available doses, and what to expect.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 for Weight Management
Mounjaro is a dual GIP and GLP-1 receptor agonist—meaning it activates two natural hormone pathways that regulate eating behaviour and blood sugar. GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) are hormones your gut naturally produces after eating.
When activated, these pathways signal to your brain that you are full, reducing hunger and food cravings. Mounjaro also slows how quickly food leaves your stomach, which typically means you feel satisfied after eating smaller portions. Additionally, it supports your body's ability to use fat for energy.
Key effects:
- Reduced appetite and fewer food cravings
- Increased feeling of fullness after smaller meals
- Slower gastric emptying (digestion)
- Better blood sugar control
- Improved fat utilisation
Mounjaro is not insulin and does not work like diabetes medication—it is specifically designed to help with weight management. Results appear gradually over weeks and months, not overnight, and weight loss requires consistent use alongside lifestyle changes.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 Eligibility and How to Access Mounjaro
You may be eligible for Mounjaro in the UK if you have:
- A BMI of 30 kg/m² or above (obesity), OR
- A BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, high blood pressure, high cholesterol, sleep apnoea, or cardiovascular disease history)
- For South Asian, Chinese, Black African, or Black Caribbean adults: lower thresholds may apply (from BMI 27.5+)
Access Mounjaro through NHS specialist tier 3 weight management services (referral from your GP) or private online prescribing (following clinical assessment with a UK-licensed prescriber). Use our free GLP-1 weight loss calculator to explore potential outcomes, and check your BMI with our BMI calculator to understand your starting point.
- 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.
What weight loss can I expect with Mounjaro in the UK?
Clinical trials (SURMOUNT-1) showed average weight loss of approximately 15–21% of body weight over 72 weeks, depending on dose. At the maximum dose of 15 mg weekly, average loss was 20.9%. However, individual results vary significantly based on adherence, diet, physical activity, and personal metabolism. Weight loss is not assured, and some people lose more or less than the average.
How often do I inject Mounjaro?
Mounjaro is a once-weekly injection. You use a pre-filled KwikPen device to inject 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, or 15 mg under the skin (abdomen, thigh, or upper arm). Each pen contains 4 weekly doses. You gradually increase your dose every 4 weeks until reaching your target maintenance dose.
Is Mounjaro available on the NHS in the UK?
Yes, NICE has approved tirzepatide (Mounjaro) for weight management within NHS specialist services. However, NHS access is limited to tier 3 specialist weight management services and availability varies significantly by region. Waiting lists can be very long. Private access is available through online prescribing services, though this requires payment (typically £129–£320+ monthly depending on dose).
What are the common side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain—especially when starting or increasing doses. These often improve over time as your body adjusts. Less common effects include headache, fatigue, dizziness, injection site reactions, and hair loss. Serious side effects are rare but include severe stomach pain (pancreatitis) and severe allergic reactions—seek immediate medical attention if these occur.
Is Mounjaro better than Wegovy for weight loss?
Mounjaro and Wegovy (semaglutide) are both prescription weight management injections with similar average weight loss outcomes. Mounjaro uses a dual GIP + GLP-1 mechanism, whilst Wegovy uses GLP-1 only. Clinical trials suggest Mounjaro may have a slight edge in average weight loss, but differences are modest and individual response varies greatly. Your prescriber will recommend the most suitable option based on your health profile.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.