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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Stomach Weight Loss: UK Prescription Medication Options
Weight loss medication available in the UK can help adults manage their weight through prescription injections. These medicines work by reducing appetite and helping you feel fuller for longer. If you're interested in weight management through medication, understanding your options and eligibility is the first step. The NHS offers specialist weight loss services, and private options are also available for eligible adults. This guide explains the main prescription medications available, how they work, and how to find out if you might be suitable for treatment.
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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-only GLP-1 medications are currently licensed in the UK for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Each works by activating natural hormone pathways that regulate appetite and blood sugar control. Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy and Saxenda are GLP-1 agonists only.
In clinical trials, adults using these medications alongside a reduced-calorie diet and increased physical activity experienced average weight losses of 14–21% of their body weight. Individual results vary significantly. Mounjaro is injected once weekly, Wegovy is injected once weekly, and Saxenda requires a daily injection.
To check your BMI and understand where you currently fall on NHS weight categories, use our free BMI calculator above. Eligibility for prescription weight loss medication typically requires a BMI of 30 or above, or 27 or above if you have weight-related health conditions such as type 2 diabetes, high blood pressure, or heart disease.
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 Access vs Private Options
NHS access to weight loss medication is through tier 3 specialist weight management services. You'll need a GP referral, though waiting lists vary significantly by region—some areas have waits of several months or longer. Private prescribing through GPhC-registered online pharmacies is faster and doesn't require an NHS referral, though costs typically range from £129 to £320 per month depending on the dose.
Both routes require a clinical assessment to confirm you're suitable for treatment. Your prescriber will review your medical history, current medications, and health conditions. If you're interested in exploring weight loss medication, start by speaking with your GP. They can discuss whether medication might be appropriate for you and explain local NHS options. Track your progress with our free progress tracker as you work towards your goals.
- 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 prescription weight loss medications are available in the UK?
Three medications are licensed for weight management in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All are GLP-1 or dual GIP/GLP-1 receptor agonists that reduce appetite and help you feel fuller. They're all prescription-only and require a clinical assessment before being prescribed.
Who is eligible for weight loss medication in the UK?
You may be eligible 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. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds may apply. Your GP or prescriber will assess individual eligibility.
How much weight can I expect to lose with these medications?
Clinical trials showed average weight losses of 14–21% of body weight when used alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly. Weight loss is not assured, and results depend on your adherence to lifestyle changes and how your body responds.
Can I access weight loss medication through the NHS?
Yes, through tier 3 specialist weight management services. You'll need a GP referral. Availability and waiting times vary by region—some areas have longer waits. Private options are also available through licensed online prescribers without an NHS referral, though these involve a cost.
What are the common side effects of weight loss injections?
Nausea, diarrhoea, vomiting, and constipation are very common, especially when starting or increasing doses. Most side effects are temporary and improve over time. Indigestion, fatigue, and injection site reactions are also common. Serious side effects are rare but require immediate medical attention.
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.