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
Free tracker included with every download this week
What Are Effective Weight Loss Pills in the UK?
Effective weight loss pills in the UK are prescription-only medications that may help reduce appetite and support weight loss alongside lifestyle changes. The most commonly prescribed options are GLP-1 receptor agonist injections like Wegovy (semaglutide) and Mounjaro (tirzepatide), which work differently to traditional diet pills. Unlike unproven over-the-counter supplements, these medicines have been tested in clinical trials and are regulated by the MHRA. Access through the NHS or private prescribing requires a clinical assessment to ensure they're safe and appropriate for your individual health needs.
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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.
How Do Prescription Weight Loss Medications Work?
GLP-1 receptor agonists like Wegovy are the most effective prescription weight loss medications available in the UK. They work by activating the GLP-1 hormone pathway, which naturally signals to your brain that you're full, reducing appetite and food cravings. This helps you eat smaller portions and feel satisfied sooner.
- Slows how quickly food leaves your stomach, extending the feeling of fullness
- Reduces the desire to snack between meals
- May help regulate blood sugar levels
- Clinical trials showed an average weight loss of around 15% body weight over 68 weeks
Mounjaro (tirzepatide) works via a dual mechanism, activating both GIP and GLP-1 pathways, with clinical trials showing average weight loss of approximately 15–21% body weight. Important: these are prescription-only medicines requiring a clinical assessment. Individual results vary, and they work best alongside a reduced-calorie diet and increased physical activity.
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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.
Are Weight Loss Pills Available on the NHS?
Yes, prescription weight loss medications are available through the NHS, but access is typically through specialist tier 3 weight management services rather than standard GP prescription. You'll need to be referred by your GP to these services, which assess your eligibility based on your BMI and any weight-related health conditions.
However, NHS waiting lists for specialist services can be lengthy in many areas. Private access is also available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. Whether you choose NHS or private prescribing, ensure you receive proper medical supervision and combine any weight loss medication with lifestyle changes for best results.
- 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 makes a weight loss pill "effective" in the UK?
An effective weight loss pill must be prescription-only, regulated by the MHRA, and supported by clinical trial evidence. Medications like Wegovy have been tested in controlled trials (STEP trials) showing consistent weight loss results. They're effective because they address appetite control rather than relying on stimulants, and work best alongside diet and exercise changes rather than as a standalone solution.
Is Ozempic the same as Wegovy for weight loss?
No. Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (up to 2mg doses), while Wegovy is specifically approved for weight management (up to 2.4mg). Ozempic is not licensed for weight loss in the UK — using it off-label for weight loss is not recommended. Always use the medication licensed for your specific indication.
How much weight can I expect to lose with prescription pills?
Clinical trial data shows Wegovy helps an average of clinically studied weight loss, and Mounjaro around 15–21%, but individual results vary significantly. Some people lose more, others less. Results depend on your starting weight, adherence to the medication, diet quality, physical activity level, and individual metabolism. Your GP or prescriber can discuss realistic expectations for your situation.
Do I need to diet and exercise while taking weight loss pills?
Yes. Prescription weight loss medications are most effective when combined with a reduced-calorie diet and increased physical activity. They're not replacements for lifestyle changes — they're tools to help you stick to healthier habits by reducing appetite and cravings. The NHS recommends losing no more than 0.5–1kg per week for sustainable results.
Can I get weight loss pills without a prescription in the UK?
No legitimate, effective weight loss pills are available over-the-counter in the UK. Unproven supplements and slimming pills sold without prescription have not undergone rigorous clinical testing. Prescription medications like Wegovy and Mounjaro require a formal clinical assessment to ensure they're safe for you. Always consult your GP or a licensed prescriber rather than buying unregulated products online.
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.