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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Best Drugs for Losing Weight in the UK
If you're looking for the most effective prescription weight loss medications available in the UK, there are several licensed options that may help. These include GLP-1 and GIP/GLP-1 receptor agonist injections, which work by helping regulate appetite and support feeling fuller after meals. All prescription weight loss drugs require a clinical assessment and must be used alongside dietary changes and increased physical activity for best results. This guide covers the evidence, how they work, eligibility criteria, and what sustainable weight loss actually means for UK adults.
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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.
Prescription Weight Loss Medications Licensed in the UK
Three prescription-only weight loss medications are currently licensed for use in the UK:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist injected once weekly. Clinical trials (SURMOUNT-1) showed average weight loss of 15–21% body weight over 72 weeks at maximum dose, alongside a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — a GLP-1 receptor agonist injected once weekly. Clinical trials (STEP-1) showed average weight loss of approximately 15% body weight at 68 weeks, though individual results vary significantly.
- Saxenda (liraglutide) — a GLP-1 receptor agonist injected daily, typically reserved for specific clinical situations in the UK.
All three work by activating natural hormone pathways that signal satiety (feeling full) and help regulate appetite. They slow how quickly food leaves your stomach and may reduce food cravings. Importantly, these are prescription-only medicines requiring clinical assessment and a prescription from a licensed GP or prescriber.
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.
Eligibility and Access in the UK
To be eligible for prescription weight loss drugs in the UK, you typically need a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition (type 2 diabetes, high blood pressure, cardiovascular disease, or sleep apnoea). For South Asian, Chinese, Black African, and Black Caribbean adults, lower BMI thresholds apply due to higher health risks at lower weights.
Access routes include NHS specialist tier 3 weight management services (via GP referral, though waiting lists vary by region) or private prescribing through licensed online providers following a clinical consultation. Our GLP-1 weight loss calculator can help you understand potential outcomes at different doses, while our BMI calculator lets you check where you currently fall on NHS guidelines.
Weight loss through prescription medication should always be combined with sustainable lifestyle changes — reduced calorie intake and regular physical activity — for the best long-term results. The NHS recommends losing weight at a rate of 0.5–1 kg per week as sustainable. Even a 5–10% reduction in body weight can deliver meaningful health benefits, including improved blood pressure, better blood sugar control, and reduced joint pain. Track your progress using our free progress tracker to monitor both weight and how you feel as changes take effect.
- 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 the difference between Mounjaro and Wegovy for weight loss?
Both are prescription-only, once-weekly injections. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials showed Mounjaro users lost on average 15–21% body weight, compared to approximately 15% for Wegovy, but individual results vary considerably. Your prescriber will assess which is most suitable based on your health profile.
Are prescription weight loss drugs available on the NHS?
Yes, Mounjaro and Wegovy are approved for NHS use through specialist tier 3 weight management services. However, access varies significantly by region, and waiting lists can be lengthy. Private prescribing through GPhC-registered providers is also available without NHS referral, though this involves costs. Your GP can discuss which route is best for you.
What are the main side effects of weight loss injections?
Common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — typically most noticeable when first starting or increasing doses. Most people adapt over time. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or allergic reactions. Always inform your prescriber of any persistent or severe symptoms.
How quickly do prescription weight loss drugs work?
Weight loss typically becomes noticeable within 4–8 weeks of starting treatment, though this varies individually. Most people experience gradual, sustained loss over several months. Your prescriber will assess progress and adjust doses as needed. Combining medication with a reduced-calorie diet and physical activity produces the best outcomes.
Do I need to follow a diet while taking weight loss medication?
Yes. Prescription weight loss drugs are most effective when used alongside a reduced-calorie diet and regular physical activity. These medications help regulate appetite and support feeling fuller, but they work best as part of a comprehensive lifestyle approach. Your prescriber or a dietitian can help design a sustainable plan tailored to you.
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.