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 Programs, Gym, and Prescription Medication in the UK
Many people combine gym routines and structured weight loss programs for sustainable results. However, for some adults, prescription weight management medication may also be helpful. The UK has several licensed prescription options available — Mounjaro, Wegovy, and Saxenda — alongside lifestyle changes. This guide explains how prescription weight loss medication works in the UK, who may be eligible, and how to find out if it's right for you through the NHS or private prescribing.
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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 Prescription Weight Loss Options
Three main prescription medications for weight loss are currently licensed in the UK:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 injection given once weekly. In clinical trials, participants lost an average of 15–21% of their body weight over 72 weeks alongside diet and exercise.
- Wegovy (semaglutide) — a GLP-1 receptor agonist injection given once weekly. Clinical data showed average weight loss of approximately 15% of body weight at the maximum dose.
- Saxenda (liraglutide) — a GLP-1 injection given once daily, with similar weight loss outcomes to Wegovy.
All three are prescription-only and require a clinical assessment before being prescribed. Eligibility typically applies to adults with a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. These medications work alongside reduced-calorie diet and increased physical activity — they are not replacements for lifestyle changes.
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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.
How to Access Weight Loss Medication in the UK
Access to prescription weight loss medication in the UK depends on your route:
- NHS route: Speak to your GP about referral to a tier 3 specialist weight management service. NHS access varies significantly by region and can involve waiting lists.
- Private route: Online consultations with UK-licensed prescribers are available without NHS referral. A clinical assessment determines eligibility, and prescriptions are dispensed by GPhC-registered pharmacies.
Regardless of route, a healthcare professional will assess your BMI, weight-related health conditions, and suitability before prescribing. Use our free BMI calculator above to check your starting point, and speak with your GP about whether prescription weight loss medication might support your weight management goals alongside gym routines and dietary changes.
- 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.
Can I use weight loss medication while going to the gym?
Yes, prescription weight loss medications like Mounjaro and Wegovy are designed to be used alongside increased physical activity and a reduced-calorie diet. Exercise is an important part of sustainable weight management. Your GP or prescriber will advise you on balancing medication, diet, and exercise for best results.
How do I know if I'm eligible for prescription weight loss medication in the UK?
Eligibility typically requires a BMI of 30 or above, or 27 or above with at least one weight-related health condition (such as type 2 diabetes, high blood pressure, or heart disease). Use our free BMI calculator to check your starting point, then speak to your GP about whether you may qualify for prescription options.
What's the difference between Mounjaro and Wegovy for weight loss?
Both are once-weekly injections licensed for weight loss in the UK. Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is a GLP-1 agonist only. Clinical trials suggest similar average weight loss outcomes (15–21% for Mounjaro, around 15% for Wegovy), though individual results vary. A prescriber will help determine which is more suitable for you.
How quickly can I expect weight loss with prescription medication?
Weight loss is typically gradual. Clinical trials showed average losses of 15–21% of body weight over 68–72 weeks alongside diet and exercise. The first few weeks may show minimal change as the body adjusts. Weight loss varies between individuals, and results depend on dose, adherence, diet, and activity level.
Can I get weight loss medication on the NHS?
Yes. NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for use within NHS specialist weight management services (tier 3). Access is via GP referral and varies significantly by region. Private online prescribing is also available without NHS referral. Both routes require clinical assessment and a prescription from a licensed healthcare professional. ```
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.