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
Weight Loss Medications Available in the UK
Several prescription medications for weight management are now available to UK adults, helping support weight loss alongside diet and exercise. The most commonly prescribed are GLP-1 receptor agonist injections — medications that mimic a natural hormone to help reduce appetite and support feeling fuller after smaller meals. Access varies between NHS specialist services and private prescribing, and eligibility depends on your BMI and health circumstances. This guide explains how these medications work, who can access them, and what to expect.
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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 dual GIP and GLP-1 receptor agonist injected once weekly, maximum dose 15 mg. Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks when combined with a reduced-calorie diet and physical activity.
- Wegovy (semaglutide) — a GLP-1 receptor agonist injected once weekly, maximum dose 2.4 mg. The STEP trial demonstrated average weight loss of approximately 15% of body weight at 68 weeks.
- Saxenda (liraglutide) — a GLP-1 receptor agonist injected once daily, maximum dose 3 mg. Effective for weight management, though less commonly prescribed than the weekly injections.
All three are prescription-only and require a clinical assessment before being prescribed. Try our free GLP-1 weight loss calculator to explore how these medications might support your weight loss journey with 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.
Who Can Access Weight Loss Medications in the UK?
Eligibility for prescription weight loss medication depends on your BMI and health profile. Generally, you may be eligible 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, abnormal cholesterol, or sleep apnoea. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply due to higher cardiovascular risk at lower weights. Both NHS specialist weight management services and private prescribers assess eligibility individually. Use our free BMI calculator to check your current BMI and see where you sit on NHS weight management guidelines.
- 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.
How do weight loss injections work?
GLP-1 medications mimic a natural gut hormone that signals fullness to your brain, reduces appetite, and slows how quickly food leaves your stomach. This helps you eat smaller portions and feel satisfied sooner. Mounjaro (tirzepatide) works on two pathways (GIP and GLP-1), while Wegovy and Saxenda work on the GLP-1 pathway alone.
What's the difference between Ozempic and Wegovy?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (doses up to 2 mg) and is not approved for weight loss in the UK. Wegovy is the licensed weight management version at higher doses (up to 2.4 mg). Using Ozempic for weight loss would be off-label. Always use the medication specifically prescribed for you.
Can I get weight loss medications through the NHS?
Yes, but access is through specialist tier 3 weight management services — not routine GP prescription. You'll need a referral from your GP. Availability varies significantly by region and waiting lists can be long. Private prescribing through GPhC-registered pharmacies is an alternative if you prefer faster access.
How much weight can I expect to lose?
Clinical trials showed average weight loss of 15–21% of body weight over several months, though individual results vary significantly. Some people lose more, others less. Weight loss depends on your starting weight, diet adherence, physical activity, and how your body responds. Your prescriber can discuss realistic expectations based on your circumstances.
What are the main side effects of weight loss injections?
Very common side effects include nausea, diarrhoea, constipation, and stomach pain — these often reduce as your body adjusts. Less common are dizziness, fatigue, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Always report new symptoms to your prescriber.
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.