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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Weight Loss Medication in the UK — 3-Month Overview
Achieving meaningful weight loss in three months is possible with the right approach, and for eligible adults in the UK, prescription medication can support this journey. Weight management medications like Mounjaro and Wegovy are now available through both NHS specialist services and private prescribing, offering evidence-based options alongside lifestyle changes. This guide explains what's available, who qualifies, and how to explore these options with your GP or healthcare provider.
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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.
UK Prescription Weight Loss Options
Three prescription-only medications are currently licensed for weight management in the UK:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist that works by reducing appetite and supporting feeling fuller after meals. In clinical trials, people taking Mounjaro lost an average of 15–21% of their body weight over time.
- Wegovy (semaglutide) — a GLP-1 receptor agonist given as a once-weekly injection. Clinical trial data showed average weight loss of around 15% of body weight when combined with reduced-calorie eating and physical activity.
- Saxenda (liraglutide) — a once-daily GLP-1 injection that has been available longer than the weekly options.
All are prescription-only and require clinical assessment before being prescribed. Individual results vary significantly — some people lose more, some less. These medications work best when combined with dietary changes and increased physical activity, not as a replacement for lifestyle changes. Many people see measurable progress within the first three months, though results depend on dose, adherence, and individual factors.
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.
NHS vs Private Access in the UK
NHS Access: Weight loss medications are available through NHS specialist tier 3 weight management services. You'll need referral from your GP, and availability varies significantly by region. NHS waiting lists can be lengthy, sometimes several months or longer depending on your area.
Private Access: Prescription medications are available through GPhC-registered online prescribers following a clinical assessment. This route doesn't require NHS referral and is often faster, though there is a cost involved (typically £100–£300+ monthly depending on dose).
The first step is a conversation with your GP about whether you might be eligible and which route suits your situation. Your GP can assess your BMI, health conditions, and current circumstances, then either refer you to specialist NHS services or advise on private options.
- 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 BMI do I need to be eligible for prescription weight loss medication in the UK?
Generally, adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions (like type 2 diabetes or high blood pressure) may be eligible. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds may apply. Your GP can assess your individual eligibility.
How much weight can I realistically expect to lose in 3 months?
With prescription medication alongside lifestyle changes, people often see 2–4 kg loss per month on average, though individual results vary significantly. Some lose more, some less. Three months is often enough time to reach an effective dose and see meaningful progress, but the medication continues to work over longer timeframes.
Do I need to change my diet and exercise when taking weight loss medication?
Yes — prescription weight loss medications are most effective when combined with a reduced-calorie diet and increased physical activity. Medication alone is not sufficient. The NHS recommends working with a healthcare provider on a full lifestyle approach.
Can I get weight loss medication on the NHS or do I need to go private?
Both options exist in the UK. NHS access is through specialist tier 3 weight management services — you'll need a GP referral, but there's no medication cost. Private access is available through online prescribers following a clinical assessment, typically faster but with a cost. Ask your GP which route is appropriate for you.
What are the most common side effects of Mounjaro or Wegovy?
Nausea, diarrhoea, constipation, and stomach discomfort are common, especially in the first few weeks. These often improve as your body adjusts. Serious side effects are rare but can include severe stomach pain or allergic reactions — seek medical attention immediately if these occur. Always discuss potential side effects with your prescriber.
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.