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
Safe Weight Loss Medication in the UK
Weight loss medication can be a safe and effective option for managing excess weight when prescribed by a qualified healthcare professional. In the UK, prescription weight loss medications are available through NHS specialist services and private prescribing, following a clinical assessment. These medications work alongside lifestyle changes — not instead of them — to help support sustainable weight management. Understanding how they work, what to expect, and whether you're eligible is important before considering this option.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
How Safe Weight Loss Medications Work
The most commonly prescribed weight loss medications in the UK are GLP-1 receptor agonists — medications that mimic a natural hormone your body produces after eating. These medications help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals.
- Wegovy (semaglutide) — a once-weekly injection, average weight loss around 15% of body weight in clinical trials
- Mounjaro (tirzepatide) — a once-weekly injection with dual GIP and GLP-1 action, average weight loss 15–21% in clinical trials
- Saxenda (liraglutide) — a once-daily injection option
All are prescription-only medicines requiring assessment by a licensed prescriber. Individual results vary significantly, and weight loss typically occurs alongside a reduced-calorie diet and increased physical activity.
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 Can Access Weight Loss Medication in the UK
You may be eligible for prescription weight loss medication in the UK 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 cardiovascular disease. Lower BMI thresholds (from 27.5) apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, as these groups face higher health risks at lower weights.
Access through the NHS requires referral to a tier 3 specialist weight management service, with potential waiting lists. Private access is available through GPhC-registered online pharmacies following an online clinical assessment. Your GP or a licensed prescriber can advise whether this option is right for you.
- 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.
Are weight loss medications safe?
When prescribed appropriately by a healthcare professional, weight loss medications are generally safe. All GLP-1 medications available in the UK have undergone clinical trials and regulatory approval. Side effects are common (nausea, diarrhoea) but usually temporary. Serious side effects are rare. Always discuss medical history and current medications with your prescriber before starting.
How much weight can I expect to lose?
Clinical trial averages show weight loss of 15–21% of body weight, but individual results vary significantly. Some people lose more, others less. Weight loss depends on adherence to medication, diet changes, physical activity, metabolism, and genetics. MyWeightCheck's GLP-1 weight loss calculator can help you understand potential projections at different doses.
Can I get weight loss medication on the NHS?
Yes, but access is limited to NHS specialist tier 3 weight management services, typically requiring a GP referral. Availability and waiting times vary significantly by region. Private prescribing offers faster access but comes at cost. Contact your GP to discuss NHS eligibility and referral options in your area.
What's the difference between Wegovy and Mounjaro?
Wegovy (semaglutide) is a single GLP-1 receptor agonist; Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist. Both are once-weekly injections. Mounjaro typically shows slightly higher average weight loss in trials, but both are effective. Your prescriber will assess which suits you best based on your health profile.
Do I need to change my diet and exercise?
Yes. Weight loss medications are most effective when combined with lifestyle changes — reduced-calorie diet and increased physical activity. The medication supports these changes by reducing appetite and cravings, but it's not a standalone solution. A holistic approach yields the best sustainable results.
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.