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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Weight Loss Pills in the UK — What You Need to Know
If you're looking to buy weight loss pills in the UK, you should know that prescription weight management medication is available through both NHS and private routes for eligible adults. The UK has three licensed prescription options: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These aren't over-the-counter tablets — they're prescription-only medicines that require a clinical assessment to establish eligibility. Understanding your options and how to access them is an important first step in your weight management journey.
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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:
- Mounjaro (tirzepatide) — A once-weekly injection that works as a dual GIP and GLP-1 receptor agonist. Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks, though individual results vary significantly.
- Wegovy (semaglutide) — A once-weekly GLP-1 injection. Clinical evidence suggests an average weight loss of around 15% of body weight when combined with lifestyle changes.
- Saxenda (liraglutide) — A once-daily GLP-1 injection. Typically associated with modest weight loss results compared to the weekly options.
All three require a prescription from a UK-licensed healthcare professional. Eligibility depends on your BMI and overall health status. Use our free BMI calculator to check where you fall on the UK health scale, and our GLP-1 weight loss calculator to explore potential outcomes at different doses.
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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.
NHS vs Private Access in the UK
NHS access to weight loss medication is through specialist tier 3 weight management services, typically involving a GP referral. Availability and waiting times vary significantly by region (ICB). Some areas have very long waiting lists, whilst others offer faster access.
Private access is available through GPhC-registered online prescribing services following an online clinical assessment. This route doesn't require an NHS referral and is often faster, though you'll pay out of pocket (typically £129–£320+ per month depending on dose and medication).
Either way, a licensed prescriber must assess whether weight loss medication is suitable for you. Start by speaking to your GP about your weight management goals — they can advise on NHS eligibility 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.
Who is eligible for prescription weight loss medication in the UK?
Adults with 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), may be eligible. Lower thresholds apply to South Asian, Chinese, Black African, and Black Caribbean adults due to higher health risks at lower BMI. A healthcare professional must assess your individual circumstances.
Can I buy weight loss pills over the counter in the UK?
No. Mounjaro, Wegovy, and Saxenda are all prescription-only medicines in the UK. They're not available without a prescription from a licensed healthcare professional. Over-the-counter weight loss supplements exist, but prescription medication offers stronger clinical evidence for meaningful weight loss.
How quickly will I see results from weight loss medication?
Most people begin to notice weight loss within 4–8 weeks of starting treatment, though this varies. Clinical trials show average weight loss of 15–21% over several months when medication is combined with reduced-calorie diet and increased physical activity. Individual results vary significantly — some people lose more, some less.
What's the difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist (once weekly), whilst Wegovy is a GLP-1 agonist only (also once weekly). Clinical data suggests Mounjaro may produce slightly greater average weight loss, but both are effective. Individual response varies. Your prescriber will recommend based on your health profile.
Do I need to stay on weight loss medication forever?
No, but weight loss medication is typically a long-term tool, not short-term. Many people maintain weight loss whilst taking it and may regain weight if they stop. Your prescriber will discuss the right duration for your situation and help you plan a sustainable approach alongside lifestyle changes.
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.