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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Fast Weight Loss Plan: UK Prescription Options
If you're looking for a fast weight loss plan in the UK, prescription medications may be an option worth discussing with your GP. Weight loss injections like Mounjaro and Wegovy are licensed in the UK for adults with obesity or overweight combined with weight-related health conditions. This guide explains how these prescription weight management options work, who is eligible, and how to access them through either NHS specialist services or private prescribing.
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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 Weight Loss Medications
The UK has three prescription-only medications approved for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro is a dual GIP and GLP-1 receptor agonist — in clinical trials, participants lost an average of 15–21% of their body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity. Wegovy, a GLP-1 agonist, showed similar results in clinical trials with an average weight loss of approximately 15% of body weight.
Eligibility criteria: 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, or sleep apnoea. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds. Individual results vary significantly, and these medications work best alongside lifestyle changes. Always consult your GP or a licensed prescriber to assess whether prescription weight loss medication is appropriate for you.
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 vs Private Access in the UK
NHS access: You can ask your GP for referral to a tier 3 specialist weight management service. NICE has approved tirzepatide (Mounjaro) for use within NHS specialist services, though regional availability and waiting lists vary — some areas have waiting times of several months or longer.
Private access: UK-licensed online prescribers can assess your eligibility following an online consultation and issue a prescription if appropriate. This route does not require NHS referral and is available more quickly than NHS specialist services. Costs vary by medication, dose, and provider. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses, and our BMI calculator to check your personal BMI against NHS eligibility thresholds.
- 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 fastest prescription weight loss medication in the UK?
Mounjaro (tirzepatide) showed slightly higher average weight loss in clinical trials (15–21%) compared to Wegovy (approximately 15%), but individual results vary significantly. Speed of weight loss depends on the dose, your metabolism, diet, and activity level. Results are not assured, and sustainable weight loss typically occurs at 0.5–1 kg per week.
Am I eligible for fast weight loss medication on the NHS?
You may be eligible if your BMI is 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. South Asian, Chinese, Black African, and Black Caribbean adults qualify at lower BMI thresholds. Your GP can assess your individual eligibility and refer you to a specialist weight management service.
How much weight can I lose with Mounjaro or Wegovy?
Clinical trials showed average weight loss of 15–21% for Mounjaro and approximately 15% for Wegovy over 12–18 months, alongside a reduced-calorie diet and increased physical activity. Individual results vary based on dose, adherence, genetics, and lifestyle. Weight loss is not assured, and some people may lose more or less than average.
Can I get prescription weight loss medication quickly in the UK?
Private online prescribing typically offers faster access (days to weeks) compared to NHS specialist services, which may have waiting lists of several months in many areas. Both routes require clinical assessment and a prescription from a UK-licensed prescriber. Cost varies — NHS prescription is free for eligible patients; private costs range from approximately £129–£320 per month depending on dose and provider.
What should I do if I think I need a fast weight loss plan?
Start by speaking with your GP about your weight management goals. Your GP can assess your BMI, health conditions, and eligibility for prescription medication. They can refer you to NHS specialist services or you can explore private online prescribing options. Weight management works best with support — your GP can also recommend diet, exercise, and behaviour change strategies alongside medication if appropriate.
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.