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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Quick Weight Loss Diet: UK Prescription Medication Options
If you're looking for quick weight loss diet support in the UK, prescription medications are now available through the NHS and private clinics. GLP-1 receptor agonist injections like Mounjaro and Wegovy can help alongside diet and exercise. However, these aren't quick fixes—they're tools to support sustainable weight loss over months. This guide explains prescription options available to UK adults, how they work, and whether you might be eligible. Always discuss any weight loss approach with your GP first.
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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 Options
Three prescription-only medications are licensed in the UK for weight management alongside a reduced-calorie diet and physical activity:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist. Once-weekly injection. Average weight loss in clinical trials: 15–21% of body weight. Doses range from 2.5 mg to 15 mg weekly.
- Wegovy (semaglutide) — a GLP-1 receptor agonist. Once-weekly injection. Average weight loss: approximately 15% of body weight. Maximum dose: 2.4 mg weekly.
- Saxenda (liraglutide) — a GLP-1 receptor agonist. Daily injection. Maximum dose: 3 mg daily.
All three require a prescription from a UK-licensed prescriber following a clinical assessment. Individual results vary significantly. These medications work by reducing appetite and helping you feel fuller after smaller meals, but they're not a replacement for diet and exercise changes.
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 a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds due to higher health risks. Start by speaking with your GP, who can refer you to a specialist weight management service (NHS tier 3) or you can access private prescribing through a UK-licensed online clinic. Use our free BMI calculator above to check your starting point, and our GLP-1 weight loss calculator to explore potential results at different doses.
- 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.
Is quick weight loss with medication safe?
Prescription weight loss medications like Mounjaro and Wegovy are safe when prescribed by a qualified healthcare professional following clinical assessment. The NHS recommends losing 0.5–1 kg per week for sustainable results. Faster weight loss is possible with medical support but should always be monitored by your GP or prescriber.
How long does it take to see results with weight loss medication?
Clinical trials show that weight loss typically begins within 2–4 weeks of starting medication. Most significant results appear after 8–12 weeks of consistent use alongside reduced-calorie diet and exercise. Full results can take 6–12 months. Individual timelines vary.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) uses a dual GIP and GLP-1 mechanism and showed average weight loss of 15–21% in trials. Wegovy (semaglutide) uses GLP-1 alone and showed approximately 15% average weight loss. Mounjaro has a higher maximum dose (15 mg vs 2.4 mg). Both require clinical assessment to determine which is suitable for you.
Can I get weight loss medication on the NHS?
Yes. The NHS prescribes tirzepatide (Mounjaro) and semaglutide (Wegovy) through specialist tier 3 weight management services. Access varies by region and waiting lists can be long. Your GP can refer you, or you can pursue private prescribing through a GPhC-registered online clinic.
Are there side effects with weight loss injections?
Common side effects include nausea, diarrhoea, constipation, and stomach pain—usually mild and temporary. Serious side effects are rare but can include pancreatitis (severe stomach pain). Your prescriber will discuss all risks and monitor you during treatment. Report any concerning symptoms to your GP immediately.
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.