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
Step by Step Weight Loss: UK Prescription Medication Guide
Weight loss is a gradual process that works best with the right support. For many UK adults, this now includes prescription weight management medications alongside lifestyle changes. This guide walks you through the options available, how to check if you're eligible, and how to start a conversation with your GP or healthcare provider about prescription weight loss support.
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.
UK-Licensed Prescription Weight Loss Options
Three prescription medications are currently licensed in the UK for weight management:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist, injected once weekly. In clinical trials, it helped participants lose an average of 15–21% of their body weight alongside a reduced-calorie diet and increased physical activity. Doses range from 2.5mg to 15mg.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, also injected once weekly. Clinical trials showed average weight loss of around 15% at the maximum dose of 2.4mg. Escalation takes 16–20 weeks.
- Saxenda (liraglutide) — a daily GLP-1 injection, with a maximum dose of 3mg. Less commonly prescribed in the UK but available through NHS and private routes.
All three require a prescription and are suitable only for adults who meet specific eligibility criteria. Individual results vary significantly, and weight loss medications are most effective when combined with dietary changes 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.
Am I Eligible? NHS and Private Routes Explained
You may be eligible for prescription weight loss medication 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). Check your BMI instantly using our free BMI calculator above.
NHS access: Your GP can refer you to a specialist tier 3 weight management service, though waiting lists vary by region. Private access: You can book an online consultation with a UK-licensed prescriber, who will assess your suitability following a clinical assessment. Either way, step by step weight loss begins with a conversation about your health, weight history, and goals.
Track your weight loss progress and estimate potential results using our free GLP-1 weight loss calculator, which can help you visualise outcomes at different doses. This supports informed conversations with your prescriber about realistic expectations.
- 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's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist and may produce slightly higher average weight loss (15–21%) compared to Wegovy (GLP-1 only, around 15% average). Both are once-weekly injections. The choice depends on your individual health profile and prescriber assessment. Results vary between individuals.
How quickly will I lose weight on prescription medication?
Safe, sustainable weight loss is typically 0.5–1kg per week. Prescription medications may support faster initial loss, but weight loss happens gradually over months. Most people reach their maximum weight loss after 6–12 months of treatment. Using our progress tracker can help you monitor gradual improvements in weight and wellbeing.
Do I need to change my diet if I take weight loss medication?
Yes. Prescription weight loss medications are most effective when combined with a reduced-calorie diet and increased physical activity. The medication helps reduce appetite and cravings, but lifestyle changes are essential for sustainable results. Your GP or specialist can refer you to dietitian support.
Can I get weight loss medication on the NHS?
Yes, tirzepatide and semaglutide are approved for use within NHS specialist weight management services. Access is through tier 3 services via your GP, though availability and waiting times vary significantly by region. Ask your GP about local services or explore private options if NHS access is limited in your area.
What happens if I stop taking weight loss medication?
Weight loss medications work while you're taking them. If you stop, weight can gradually return, which is why they're part of a long-term weight management approach. Your prescriber will discuss how long you'll take the medication and how to maintain results through sustained lifestyle changes.
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.