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 Rx Medication in the UK
If you're looking to manage your weight through prescription medication, several licensed options are now available in the UK. Weight loss injections and tablets can support weight management when combined with lifestyle changes, but they require a prescription and clinical assessment. This guide covers the main prescription weight loss medications available, who is eligible, and how to access them through the NHS or privately.
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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-Licensed Prescription Weight Loss Medications
Three main prescription weight management medications are currently licensed in the UK:
- Mounjaro (tirzepatide) — a once-weekly injectable dual GIP and GLP-1 receptor agonist. Clinical trials showed average weight loss of approximately 15–21% of body weight over 72 weeks when combined with a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. Evidence suggests average weight loss of around 15% of body weight in clinical trials alongside lifestyle changes.
- Saxenda (liraglutide) — a daily GLP-1 injection offering a different dosing schedule.
All three are prescription-only medications requiring assessment by a GP or licensed prescriber. Individual results vary significantly based on factors including starting weight, adherence, and lifestyle modifications. These medications may help reduce appetite, support feeling fuller after meals, and assist with weight management for eligible adults.
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 Access vs Private Weight Loss Rx Options
NHS route: Prescription weight loss medications are available through NHS specialist tier 3 weight management services, but access varies significantly by region. You'll typically need a GP referral and assessment by a multidisciplinary team. Waiting lists can be lengthy in many areas — check with your local integrated care board (ICB) for current availability.
Private route: Licensed GPhC-registered online pharmacies offer prescription weight loss medication following a clinical assessment with a UK-licensed prescriber. This route doesn't require an NHS referral and typically has shorter timescales, though costs range from approximately £129–£320 per month depending on dose and provider.
Start by discussing weight management options with your GP, who can assess your individual health needs and whether prescription medication is appropriate 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.
Who is eligible for prescription weight loss medication in the UK?
Adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions (type 2 diabetes, hypertension, cardiovascular disease, sleep apnoea), may be eligible. South Asian, Chinese, Black African, and Black Caribbean adults may be eligible at lower BMI thresholds due to higher health risks. Your GP will assess individual eligibility.
What's the difference between Mounjaro and Wegovy?
Both are once-weekly injections, but Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is a GLP-1 agonist only. Mounjaro reaches a maximum dose of 15mg; Wegovy reaches 2.4mg. Clinical trials suggest Mounjaro may produce slightly higher average weight loss, though individual results vary significantly.
How quickly will I lose weight on prescription weight loss medication?
Weight loss typically occurs gradually over weeks and months. NHS guidelines recommend safe weight loss of 0.5–1kg per week. With GLP-1 medications, some people see initial changes within 2–4 weeks, but maximum results usually appear after 3–6 months of treatment. Results depend on adherence and lifestyle changes.
Do I need to change my diet and exercise while taking weight loss medication?
Yes. Prescription weight loss medications work best alongside a reduced-calorie diet and increased physical activity. These medications support appetite control, but they are not replacements for lifestyle changes. Your prescriber will discuss dietary and exercise recommendations tailored to your circumstances.
What are the main side effects of prescription weight loss injections?
Common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — typically mild and transient. Less common are headache, fatigue, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Always report side effects to 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.