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
Eli Lilly Weight Loss Drug: What You Need to Know
Eli Lilly manufactures Mounjaro (tirzepatide), a prescription-only weight loss injection now available in the UK. Mounjaro is a dual GIP and GLP-1 receptor agonist that may help support weight management alongside a reduced-calorie diet and increased physical activity. It's administered as a once-weekly injection and is prescribed through NHS specialist weight management services or private online prescribing following a clinical assessment. Individual results vary, and like all prescription medications, it requires a prescription from a licensed healthcare professional.
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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 and Who Can Access It
Mounjaro (tirzepatide) is Eli Lilly's dual-action weight management injection that activates two hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual mechanism may help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. It also slows gastric emptying, helping you feel satisfied for longer.
In the UK, Mounjaro may be prescribed to adults with:
- BMI of 30 kg/m² or above, OR
- BMI of 27–29.9 kg/m² with weight-related health conditions (type 2 diabetes, hypertension, cardiovascular disease, sleep apnoea)
- Lower thresholds (BMI 27.5+) apply for South Asian, Chinese, Black African, and Black Caribbean adults due to higher health risks at lower BMI levels
Access is through NHS tier 3 specialist weight management services (waiting times vary by region) or private online prescribing following a clinical assessment with a licensed prescriber.
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.
Mounjaro Dosing, Weight Loss Results, and Side Effects
Mounjaro dosing starts at 2.5 mg once weekly, escalating every 4 weeks to a maximum of 15 mg weekly. Clinical trial data (SURMOUNT-1) showed average weight loss of approximately 15% body weight at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg over 72 weeks—though individual results vary significantly.
Common side effects include: nausea, diarrhoea, constipation, vomiting, and stomach pain. These often ease as your body adjusts. Serious side effects are rare but may include severe stomach pain (pancreatitis risk) or gallbladder complications. Always report persistent or severe symptoms to your prescriber. Track your weight loss journey using our free progress tracker to monitor your personal results.
- 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 available on the NHS?
Mounjaro is licensed in the UK and approved for use within NHS specialist weight management services. However, NHS access varies significantly by region and availability. Many areas have long waiting lists. Private online prescribing is available without NHS referral if you meet eligibility criteria and pass a clinical assessment.
What's the difference between Mounjaro and Wegovy?
Both are prescription weight loss injections available in the UK. Mounjaro (tirzepatide) uses dual GIP+GLP-1 mechanism, while Wegovy (semaglutide) uses GLP-1 only. Clinical trials showed Mounjaro achieved slightly higher average weight loss (up to 21% vs 15%), but individual results vary. Your prescriber will assess which is more suitable for you.
How quickly will I lose weight on Mounjaro?
Weight loss timing varies between individuals. Most people see gradual results over weeks and months rather than immediate loss. The NHS recommends healthy weight loss of 0.5–1 kg per week. Check your personal BMI and healthy weight range using our free BMI calculator to set realistic goals alongside your prescriber.
Can I get Mounjaro if my BMI is below 30?
Yes. You may be eligible if your BMI is 27–29.9 kg/m² and you have a weight-related health condition like type 2 diabetes, high blood pressure, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds. A prescriber will assess your individual eligibility.
What happens if I stop taking Mounjaro?
Weight may return if you stop the medication, especially without ongoing lifestyle changes. Mounjaro is most effective when combined with a reduced-calorie diet and increased physical activity. Your prescriber will discuss long-term management plans. Use our weight loss calculator to explore different scenarios and understand what ongoing weight management involves.
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.