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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Most Effective Weight Loss Pills Available in the UK
If you're looking for the most effective weight loss pills in the UK, prescription medications now offer clinically proven options for eligible adults. Unlike over-the-counter supplements, prescription weight management drugs are licensed by the MHRA and have undergone rigorous clinical trials. This guide explains the UK-licensed options available, how they work, and how to find out if you qualify. Weight management through medication works best alongside a reduced-calorie diet and increased physical activity.
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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
Three prescription medications are currently licensed in the UK for weight management:
- Mounjaro (tirzepatide) — A dual GIP and GLP-1 receptor agonist. In clinical trials, participants lost an average of 15–21% of their body weight. Started at 2.5 mg weekly, escalated up to 15 mg maximum.
- Wegovy (semaglutide) — A GLP-1 receptor agonist injected once weekly. Clinical trials showed average weight loss of around 15% of body weight. Doses range from 0.25 mg to 2.4 mg.
- Saxenda (liraglutide) — A daily GLP-1 injection with a maximum dose of 3 mg. Results similar to other GLP-1 medications, though it requires daily rather than weekly administration.
All three are prescription-only medicines requiring a clinical assessment before prescribing. Individual results vary significantly, and these medications are most effective when combined with lifestyle changes. Use our free GLP-1 weight loss calculator to see projected outcomes at different doses.
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.
NHS vs Private Access and Eligibility
In the UK, you can access prescription weight loss medication through two routes. NHS access is through specialist tier 3 weight management services via GP referral, though waiting lists vary significantly by region and can extend several months. Private access is available through GPhC-registered online prescribing services following a clinical assessment, without NHS referral.
To be eligible, you typically need a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may qualify at lower BMI thresholds. Talk to your GP about which option suits you and whether prescription weight management is appropriate for your health. Calculate your personal BMI using our free BMI calculator above to understand where you stand.
- 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 is the most effective weight loss pill available in the UK?
Mounjaro (tirzepatide) currently shows the highest average weight loss in clinical trials — approximately 15–21% of body weight. However, effectiveness varies between individuals. Wegovy is also highly effective with similar outcomes. Your suitability depends on your health profile and medical history, assessed by a prescriber.
Are weight loss pills available on the NHS?
Yes, prescription weight loss medications are available on the NHS through specialist weight management services. Access is via GP referral to tier 3 services, though availability and waiting times vary significantly across UK regions. Private options are also available through online prescribing services.
What are the side effects of prescription weight loss medications?
Common side effects include nausea, diarrhoea, constipation, and stomach pain — these often reduce over time. Less common effects include headache, fatigue, and injection site reactions. Serious side effects are rare but can include pancreatitis. Always discuss potential side effects with your prescriber.
How long do you need to take weight loss pills for results?
Clinical trials typically lasted 68–72 weeks to achieve peak weight loss. Many people continue medication long-term to maintain results. If you stop taking the medication, weight regain is common over 12 months. This is why sustainable lifestyle changes — diet and exercise — remain essential.
Can I get weight loss pills from any pharmacy in the UK?
No, weight loss medications are prescription-only and can only be obtained through a UK-licensed prescriber following a clinical assessment. This ensures the medication is appropriate for your individual health needs. Private online prescribing services and NHS specialist services are the two main routes to access.
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.