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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Fitness Weight Loss: UK Prescription Medication Options
If you're looking to manage your weight through fitness and lifestyle changes, prescription medications may also support your goals in the UK. Weight management is a complex health issue, and for some people, prescription medication alongside diet and exercise can help achieve sustainable results. This guide covers the prescription weight loss options available to UK adults, eligibility criteria, and how to access them through the NHS or private prescribing services.
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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 Weight Loss Medications
Three prescription medications are currently licensed in the UK for weight management in adults:
- Mounjaro (tirzepatide) — a once-weekly injection that works by activating GIP and GLP-1 hormone pathways. Clinical trials showed average weight loss of 15–21% of body weight when combined with diet and exercise.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. In clinical trials, participants lost an average of around 15% of body weight at the maximum dose.
- Saxenda (liraglutide) — a once-daily GLP-1 injection, typically used when weekly injections are not suitable.
All three are prescription-only and require a clinical assessment before being prescribed. To find out which medication might be right for you, use our free GLP-1 weight loss calculator to explore potential outcomes at different doses — though individual results vary significantly.
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 Treatment
You may be eligible for prescription weight loss medication if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply.
NHS access: Through specialist tier 3 weight management services following a GP referral. Availability and waiting times vary significantly by region. Private access: Through GPhC-registered online pharmacies offering private prescriptions — faster but at cost.
Your first step is speaking with your GP about NHS weight loss services or exploring private prescribing options. You can also use our BMI calculator to check where your weight sits relative to NHS categories.
- 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.
Are UK weight loss injections effective for fitness and health?
Clinical trials show that GLP-1 and GIP/GLP-1 medications can support significant weight loss when combined with diet and exercise. Average loss ranges from 15–21% of body weight, though results vary between individuals. They work best alongside sustainable lifestyle changes, not as replacements for fitness and nutrition.
How long does it take to see weight loss results?
Most people begin noticing changes within 2–4 weeks of starting treatment, though significant weight loss typically develops over weeks 8–12 as doses are increased. Weight loss is gradual and sustainable — aiming for 0.5–1kg per week, which is the NHS recommendation.
Can I access weight loss medication through the NHS?
Yes, but access is through specialist weight management services (tier 3), usually following a GP referral. NHS availability varies by region and waiting lists can be lengthy. Some people opt for private prescriptions for faster access.
What if I have type 2 diabetes — can I still take weight loss injections?
Yes. In fact, some of these medications also help manage blood sugar. However, if you're taking diabetes medication like insulin or sulphonylureas, doses may need adjusting. Always inform your prescriber of all medications you take.
Do I need to keep exercising and eating well while taking weight loss medication?
Yes. Prescription weight loss medications work best alongside a reduced-calorie diet and regular physical activity. They support and amplify your efforts, but lifestyle changes remain essential for sustainable, long-term weight loss and fitness improvements.
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.