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 Medication in the UK
If you're considering weight loss medication in the UK, you have several prescription options available. The most commonly prescribed medications are Mounjaro (tirzepatide) and Wegovy (semaglutide) — both are GLP-1 or dual-action receptor agonists that help reduce appetite and support weight management alongside lifestyle changes. Access is available through both NHS specialist weight management services and private prescribing pathways. This guide explains your options, eligibility criteria, and how to find out if prescription weight loss medication is right for you.
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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 main prescription weight loss medications are licensed in the UK for weight management:
- Mounjaro (tirzepatide) — A dual GIP and GLP-1 receptor agonist, given as a once-weekly injection. Starting dose 2.5 mg, maximum 15 mg weekly. Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks when combined with a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — A GLP-1 receptor agonist, given as a once-weekly injection. Starting dose 0.25 mg, building to a maximum of 2.4 mg. Clinical trials demonstrated average weight loss of approximately 15% body weight at the highest dose.
- Saxenda (liraglutide) — A GLP-1 receptor agonist, given as a daily injection (not weekly like the others). Maximum dose 3 mg daily. Effective for weight management but requires daily injections rather than weekly.
All three are prescription-only medicines requiring a clinical assessment before being prescribed. Individual results vary significantly based on adherence, diet, exercise, and personal metabolism.
Clinically BackedWeight Loss
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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 & How to Find Out If You're Eligible
NHS access: Available through specialist tier 3 or tier 4 weight management services following a GP referral. Your GP can refer you if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions (type 2 diabetes, hypertension, sleep apnoea, or cardiovascular disease). NHS availability varies significantly by region and waiting times can be several months in many areas. Eligibility thresholds may be lower for adults of South Asian, Chinese, Black African, or Black Caribbean heritage.
Private access: Available through online consultations with UK-licensed prescribers. A private prescriber will assess your health history and suitability, and if appropriate, issue a prescription dispensed by a GPhC-registered pharmacy. Private treatment typically costs £150–£300 per month depending on dose and provider.
Next step: Speak with your GP about weight loss medication options, use our free BMI calculator to check your current BMI, and discuss which pathway suits your circumstances best.
- 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 a GLP-1 receptor agonist and how does it help with weight loss?
A GLP-1 receptor agonist is a medication that mimics the natural GLP-1 hormone your gut produces after eating. It signals to your brain that you're full, reduces appetite and food cravings, and slows how quickly food leaves your stomach. This helps you eat smaller portions and feel satisfied with less food, supporting a calorie deficit needed for weight loss.
Am I eligible for prescription weight loss medication on the NHS?
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 (type 2 diabetes, prediabetes, hypertension, sleep apnoea, or cardiovascular disease). Eligibility thresholds are lower for certain ethnic groups. Ask your GP for a referral to your local specialist weight management service to be assessed.
How much weight can I expect to lose with these medications?
Clinical trials show average weight loss of 15–21% body weight with Mounjaro and around 15% with Wegovy over 68–72 weeks, combined with a reduced-calorie diet and physical activity. However, individual results vary significantly. Some people lose more, some less. Weight loss depends on adherence, diet, exercise, and personal metabolism — medication works best alongside lifestyle changes.
What are the common side effects of weight loss injections?
The most common side effects are nausea, diarrhoea, vomiting, constipation, and stomach pain, particularly when starting or increasing doses. These often improve over time. Less common side effects include fatigue, dizziness, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems — seek immediate medical attention if these occur.
Can I use the Progress Tracker to monitor my weight loss with medication?
Yes, our free Progress Tracker is ideal for monitoring your weight loss journey with prescription medication. Log your weight weekly or monthly to track your progress, see trends over time, and stay motivated. Combined with your GP's clinical monitoring, it helps you visualise your results alongside Mounjaro, Wegovy, or other weight loss treatments.
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.