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 Prescriptions in the UK — What You Need to Know
If you're struggling with weight management in the UK, prescription weight loss medication may be an option worth exploring with your GP. Several prescription-only medicines are now licensed for weight management, including GLP-1 receptor agonists like semaglutide (Wegovy) and tirzepatide (Mounjaro). These medications may help support weight loss when combined with reduced-calorie diet and increased physical activity. Access varies — you can pursue treatment through NHS specialist weight management services or private online prescribing. Understanding how these work, who's eligible, and what to expect is essential before considering this route.
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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.
Available Prescription Weight Loss Medications in the UK
Three main prescription weight loss medications are currently licensed in the UK for adult weight management:
- Wegovy (semaglutide) — A once-weekly GLP-1 injection that works by mimicking a natural gut hormone to reduce appetite and support feeling fuller after smaller meals. Clinical trials (STEP programme) showed average weight loss of around 15% body weight over 68 weeks when used alongside lifestyle changes.
- Mounjaro (tirzepatide) — A once-weekly injection that activates both GIP and GLP-1 pathways, offering a dual mechanism. SURMOUNT trial data showed average weight loss of 15–21% depending on dose.
- Saxenda (liraglutide) — A daily GLP-1 injection, less commonly prescribed now as once-weekly options are available.
All three are prescription-only medicines requiring clinical assessment before being prescribed. Individual results vary significantly based on dose, adherence, and lifestyle factors. Use our free GLP-1 weight loss calculator above to see potential 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.
Eligibility and NHS vs Private Access
In the UK, adults may be eligible for prescription weight loss treatment if they have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, cardiovascular disease, or sleep apnoea). For South Asian, Chinese, Black African, and Black Caribbean adults, lower thresholds apply due to higher health risks at lower BMI levels. NHS access is through tier 3 specialist weight management services — referral from your GP typically required, though waiting lists vary by region. Private access is available through GPhC-registered pharmacies following an online clinical assessment with a UK-licensed prescriber, without NHS referral. Check your BMI using our free BMI calculator above, then discuss options with your GP or arrange a private assessment to determine eligibility.
- 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 effective are weight loss prescriptions?
Clinical trials show average weight loss of 15–21% of body weight depending on medication and dose, alongside diet and exercise. However, individual results vary significantly. Some people lose more, others less. These medications work best as part of a comprehensive approach, not as standalone solutions. Your prescriber can discuss realistic expectations for your situation.
Are weight loss prescriptions available on the NHS?
Yes, but access is through specialist tier 3 weight management services, not standard GP prescription. You'll need referral from your GP, though availability and waiting times vary considerably by region. Private access via online prescribers is faster but costs approximately £129–£320 monthly depending on dose.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide but are different products. Wegovy is licensed specifically for weight management in the UK. Ozempic is licensed for type 2 diabetes management only — using it for weight loss is off-label. Always ensure your prescriber provides the correct licensed medication for your intended use.
Are there side effects with weight loss prescriptions?
Yes. Common side effects include nausea, constipation, diarrhoea, and stomach pain — typically mild and improving over time as your body adjusts. Serious side effects are rare but can include pancreatitis. Your prescriber will discuss all risks and monitor you during treatment.
Do I need to diet and exercise with weight loss medication?
Yes. Prescription weight loss medications work best alongside a reduced-calorie diet and increased physical activity. They're not replacements for lifestyle changes — they're tools to support your efforts. Track your progress using our free progress tracker to monitor results and stay motivated.
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.