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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When Diet and Exercise Alone Aren't Working: UK Weight Management Options
If you've been following a healthy diet and exercising regularly but still aren't seeing weight loss results, you're not alone. Many people find that lifestyle changes alone aren't enough to achieve their weight management goals. The good news is that prescription weight loss medication is now available in the UK for eligible adults. These prescription options can support your efforts alongside continued diet and exercise, helping you move towards a healthier weight and improve your overall health outcomes.
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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.
UK-Licensed Prescription Weight Loss Medications
The UK has approved three prescription-only weight loss injections for adults who meet specific eligibility criteria. These are all licensed by the MHRA and work alongside — not instead of — diet and exercise:
- Mounjaro (tirzepatide): A dual GIP/GLP-1 receptor agonist. Once-weekly injection. Clinical trials showed average weight loss of around 15–21% of body weight at the highest dose.
- Wegovy (semaglutide): A GLP-1 receptor agonist. Once-weekly injection. Clinical evidence suggests average weight loss of approximately 14.9% of body weight.
- Saxenda (liraglutide): A GLP-1 receptor agonist. Daily injection. Older option with slightly more modest results than newer alternatives.
All three work by helping regulate appetite, reduce food cravings, and support feeling fuller after meals. Individual results vary significantly. Try our free GLP-1 weight loss calculator above to explore potential outcomes at different doses, and use our free BMI calculator to assess your current starting point.
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.
Eligibility and How to Access Weight Loss Medication in the UK
You may be eligible for prescription weight loss medication in the UK if you have a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition (such as type 2 diabetes, high blood pressure, or cardiovascular disease). Lower thresholds apply for adults of South Asian, Chinese, Black African, or Black Caribbean heritage.
Access is available through two routes: NHS specialist weight management services (usually tier 3 services via GP referral, though waiting lists vary by region) or private prescribing (following an online clinical assessment with a UK-licensed prescriber). Speak to your GP about whether prescription weight loss medication might be right for you — they can refer you to specialist services or discuss private options.
- 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.
Why is diet and exercise sometimes not enough for weight loss?
Weight loss is influenced by many factors beyond diet and exercise, including genetics, hormones, metabolic rate, medications, and medical conditions. For some people, lifestyle changes alone don't produce sufficient results. Prescription weight loss medication can help by regulating appetite hormones and supporting your existing efforts. Individual responses vary significantly.
Are GLP-1 weight loss injections used instead of diet and exercise?
No. Prescription weight loss medications like Mounjaro and Wegovy are always used *alongside* diet and exercise, not as replacements. Clinical trials showed the best results were achieved when medication was combined with a reduced-calorie diet and increased physical activity. Medication alone won't produce lasting weight loss without lifestyle support.
How do I know if I'm eligible for prescription weight loss medication on the NHS?
You'll typically need a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes or high blood pressure. Eligibility criteria and availability vary by NHS region. Your GP can assess whether you meet local criteria and refer you to a specialist weight management service if appropriate.
How quickly will I lose weight on prescription weight loss medication?
Weight loss typically starts within the first few weeks, with most noticeable results between weeks 8–16 as doses are increased. Clinical trials showed average weight loss of 15–21% of body weight over 68–72 weeks, depending on the medication and dose. Your results will depend on many factors, including adherence to diet and exercise changes. Use our weight loss calculator to explore potential timelines.
Can I get weight loss medication through the NHS or do I have to go private?
Both options exist in the UK. NHS access is through tier 3 specialist weight management services, usually following a GP referral — though waiting lists and availability vary significantly by region. Private prescribing is available through UK-licensed online prescribers, usually faster but involves out-of-pocket costs. Your GP can advise on both pathways and what's available in your area.
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.