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
Most Effective Weight Loss Drugs Available in the UK
If you're looking for the most effective weight loss drug available in the UK, several prescription medications have strong clinical evidence. Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide) are all licensed for weight management in UK adults. These medications work alongside a reduced-calorie diet and increased physical activity. Access varies between NHS specialist services and private prescribing. This guide explains what each medication is, how they work, who's eligible, and how to access them. Use our free GLP-1 weight loss calculator above to explore potential outcomes, and our BMI calculator to understand your starting point.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 and Clinical Evidence
Three prescription medications are currently licensed for weight management in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways to reduce appetite and support feeling fuller after meals. Clinical trials showed average weight loss of approximately 15–21% of body weight. Wegovy (semaglutide) is a GLP-1 receptor agonist with clinical trial results showing average weight loss around 15% of body weight. Saxenda (liraglutide) is also a GLP-1 agonist but administered as a daily injection rather than once-weekly, with average weight loss of 5–10% of body weight.
Individual results vary significantly. All three are prescription-only medicines requiring clinical assessment before being prescribed. They work by signalling to your brain that you're full, slowing digestion, and reducing cravings — but they work most effectively when combined with dietary changes and exercise. Side effects are common initially (nausea, diarrhoea, constipation) but often improve over time.
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 if you have a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults due to higher health risks at lower BMI levels.
NHS route: Ask your GP for referral to your local tier 3 specialist weight management service. Availability and waiting times vary by region; some areas have long waiting lists. Private route: You can access these medications through GPhC-registered online prescribers without NHS referral — a licensed prescriber will assess your suitability following a consultation. Costs range from approximately £129–£320 monthly depending on dose and provider. Either way, a clinical assessment is essential to ensure the medication is right for you.
- 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 drug available in the UK?
Mounjaro (tirzepatide) currently shows the strongest clinical trial evidence with average weight loss of 15–21% of body weight, making it highly effective for eligible adults. However, effectiveness varies by individual. Wegovy (semaglutide) shows similar results around 15%, and Saxenda (liraglutide) shows 5–10%. Your GP or prescriber can advise which is most appropriate for your circumstances.
How do I know if I'm eligible for weight loss medication in the UK?
You're generally eligible if you have a BMI of 30 or above, or 25–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or sleep apnoea. South Asian and Black African adults may qualify at BMI 27.5 or above. Use our free BMI calculator above to check your BMI, then speak to your GP about eligibility.
Can I get weight loss medication through the NHS?
Yes, but access is through tier 3 specialist weight management services via GP referral. NHS availability varies significantly by region, and waiting times can be several months to over a year in some areas. Private online prescribing offers faster access but involves paying for the medication yourself.
How much weight will I lose with these drugs?
Clinical trials show average weight loss of 5–21% of body weight depending on the medication and dose. However, individual results vary greatly. Some people lose more, others less. Weight loss is most effective when combined with a reduced-calorie diet, increased physical activity, and consistent use. Try our GLP-1 weight loss calculator to estimate potential outcomes at different doses.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro's dual mechanism may offer stronger appetite suppression. Clinical trials suggest slightly higher average weight loss with Mounjaro (15–21% vs 15% for Wegovy), but both are highly effective. Choice depends on individual factors and prescriber assessment.
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.