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
Medication to Lose Weight — What You Need to Know
Prescription weight loss medications are now available on the NHS and privately in the UK, offering a medical option for people struggling with excess weight. These medications work by regulating appetite and helping you feel fuller after eating smaller portions. They're used alongside healthy weight management—not instead of it. If you've tried lifestyle changes and want to explore medication options, understanding how they work and who's eligible is an important first step. Your GP or a healthcare professional can assess whether prescription weight loss treatment 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.
Which Weight Loss Medications Are Available in the UK?
Three prescription weight loss medications are currently licensed in the UK for healthy weight management:
- Wegovy (semaglutide) — a once-weekly injection that activates the GLP-1 hormone pathway, helping regulate appetite and blood sugar control
- Mounjaro (tirzepatide) — a once-weekly injection that works on both GIP and GLP-1 pathways, offering a dual mechanism for appetite suppression
- Saxenda (liraglutide) — a daily injection, also a GLP-1 medication with a longer track record in clinical practice
All three are prescription-only medicines available through NHS specialist weight management services or private online prescribing following a clinical assessment. In clinical trials, these medications helped participants lose an average of 14–21% of their body weight when used alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly, and medication is most effective when combined with lifestyle changes.
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.
Who Is Eligible for Weight Loss Medication?
You may be eligible for prescription weight loss treatment 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). If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to increased health risks at lower weights—ask your GP about NHS health advice specific to your background.
Access through the NHS requires a referral to a specialist tier 3 weight management service, which can involve waiting lists. Private prescribing is available without NHS referral through a licensed prescriber following an online consultation. Use our free BMI calculator above to check your starting point, and discuss medication options with your GP or healthcare professional.
- 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 weight loss medications actually work?
Weight loss medications like Wegovy and Mounjaro are GLP-1 receptor agonists—they mimic a natural hormone that regulates appetite and blood sugar. They signal to your brain that you're full, reduce cravings, and slow how quickly food leaves your stomach. This helps you eat smaller portions and feel satisfied sooner, supporting a calorie deficit needed for weight loss.
What's the difference between Wegovy and Mounjaro?
Wegovy (semaglutide) is a GLP-1 agonist with a single mechanism. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, meaning it works on two appetite pathways. Both are once-weekly injections. Clinical trials show similar weight loss outcomes on average (around 15–21%), but individual response varies. Your prescriber will recommend the most suitable option for you.
Do I need to change my diet and exercise if I take weight loss medication?
Yes. Weight loss medications are most effective when combined with a reduced-calorie diet and increased physical activity. Medication supports appetite control, but sustainable weight loss requires lifestyle changes too. Think of medication as a tool to help you stick to healthier habits, not a replacement for them.
Can I get weight loss medication on the NHS?
Yes, but access is through specialist tier 3 weight management services, typically requiring a GP referral. NHS availability varies by region, and waiting lists can be lengthy. Private prescribing is an alternative—it's available immediately following an online clinical assessment with a UK-licensed prescriber.
What side effects should I expect from weight loss injections?
Common side effects include nausea, diarrhoea, constipation, and stomach pain, particularly when starting or increasing doses. These typically improve over time. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or allergic reactions. Always report unexpected symptoms to your prescriber. Use our weight converter to track your progress once you start treatment.
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.