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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Drug to Lose Weight — What You Need to Know
If you're asking about drugs to lose weight in the UK, you're likely considering prescription weight loss medications. Several drugs are licensed in the UK for weight management in adults with a BMI of 30 or above, or 27 or above with weight-related health conditions. These medications work alongside diet and physical activity changes to support sustainable weight loss. Your GP can assess whether prescription weight loss treatment is right for you, and whether you might benefit from NHS weight management support or private prescription options.
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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.
What Weight Loss Drugs Are Available in the UK?
Three prescription weight loss medications are currently licensed in the UK for weight management:
- Wegovy (semaglutide) — a once-weekly GLP-1 injection that helps reduce appetite and food cravings. Clinical trials showed average weight loss of around 15% of body weight.
- Mounjaro (tirzepatide) — a once-weekly dual GIP and GLP-1 injection. SURMOUNT trials demonstrated average weight loss of 15–21% of body weight, depending on dose.
- Saxenda (liraglutide) — a daily GLP-1 injection, available for weight loss uk support but less commonly prescribed than weekly options.
All three are prescription-only medicines requiring clinical assessment. They're not recommended as a first-line weight loss approach — the NHS emphasises diet, physical activity, and behavioural support first. These drugs are typically considered when lifestyle changes alone haven't achieved sufficient results. Our GLP-1 weight loss calculator can help you explore potential outcomes at different dose levels.
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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 Do Weight Loss Drugs Work?
Weight loss medications in the UK typically work by activating natural hormone pathways that regulate appetite and fullness signals. GLP-1 receptor agonists (Wegovy, Saxenda) mimic a hormone your gut produces after eating, signalling to your brain that you're satisfied — helping you eat less without feeling deprived. Mounjaro adds a second mechanism by also activating GIP receptors, which may enhance appetite suppression and support sustainable weight loss methods uk.
These drugs slow how quickly food leaves your stomach and may reduce cravings for high-calorie foods. Results vary between individuals, and weight loss is most effective when combined with reduced-calorie eating and increased physical activity. Check your current BMI using our free BMI calculator to understand where you sit on NHS weight management 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.
How do I get a prescription weight loss drug in the UK?
You can access prescription weight loss medication through two routes: NHS specialist tier 3 weight management services (by GP referral, though waiting lists vary) or private online prescribing through a GPhC-registered pharmacy following a clinical assessment. Either route requires a licensed prescriber to assess your health and confirm you meet eligibility criteria (BMI 30+ or 27+ with weight-related conditions). Your GP can advise which route is most appropriate.
Are weight loss drugs safe?
Prescription weight loss medications are licensed and monitored for safety by the MHRA. Common side effects include nausea, diarrhoea, and constipation — usually mild and temporary. Serious side effects are rare but can include pancreatitis or gallbladder problems. Always discuss medical history with your prescriber. These drugs are not suitable during pregnancy or for under-18s. Individual safety assessment is essential.
Will I lose weight assured with these drugs?
No. Clinical trials show these drugs help many people achieve significant weight loss (15–21% on average), but individual results vary considerably. Some people lose more, others less. Weight loss also depends on dietary changes, physical activity, and individual metabolism. These medications are tools supporting nhs weight loss programmes and lifestyle changes — not replacements for them.
How long do I need to take weight loss medication?
Duration depends on your individual health goals and how your body responds. Some people use these medications short-term to establish new habits; others continue longer-term. Your prescriber will monitor your progress and adjust treatment accordingly. Losing weight safely through sustainable lifestyle changes remains the priority — medication supports but doesn't replace this.
Can I get weight loss drugs on the NHS?
Yes. NICE has approved tirzepatide (Mounjaro) and semaglutide (Wegovy) for NHS use within specialist tier 3 weight management services. However, NHS access varies significantly by region and availability can be limited. Your GP can refer you to your local specialist service. Private prescription options are also available without NHS referral if you prefer immediate access.
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.