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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Calorie Counting And Weight Loss: Medication Options In The UK
Calorie counting is a proven weight management approach, but many UK adults find that combining dietary tracking with prescription weight loss medication offers better results. This guide covers how calorie restriction works, what GLP-1 weight loss medications are available in the UK, who is eligible for prescription support, and how to start a conversation with your GP about your options.
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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 loss options are available to eligible adults in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). All are GLP-1 or dual GIP/GLP-1 receptor agonists that work by reducing appetite, increasing feelings of fullness, and slowing gastric emptying.
- Mounjaro — dual GIP and GLP-1 agonist; once-weekly injection; doses from 2.5 mg to 15 mg; clinical trials showed average weight loss of 15–21% body weight
- Wegovy — GLP-1 agonist only; once-weekly injection; maximum dose 2.4 mg; clinical trial data showed approximately 15% average weight loss
- Saxenda — GLP-1 agonist; daily injection; maximum dose 3 mg; evidence supports 5–clinically studied weight loss alongside calorie reduction and exercise
These medications are prescribed alongside a reduced-calorie diet and increased physical activity — they are not a replacement for lifestyle changes. Your GP or a licensed prescriber will assess whether you are eligible based on your individual health.
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 Eligibility And How To Access Support
In the UK, prescription weight loss medication may be available through NHS specialist weight management services if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with a weight-related health condition such as type 2 diabetes, high blood pressure, or sleep apnoea. However, NHS access varies significantly by region and waiting times can be substantial.
Private access through GPhC-registered online pharmacies offers faster availability — you can complete an online clinical assessment and receive a prescription if appropriate, without NHS referral. Either route requires a proper clinical assessment; prescription weight loss medication is not available without this. Use our free GLP-1 weight loss calculator above to estimate potential outcomes at different doses, and speak to your GP to discuss whether medication could support your weight management goals alongside calorie tracking and lifestyle changes.
- 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.
Does calorie counting alone work for weight loss?
Yes, calorie counting can be effective — a deficit of around 500 kcal/day typically results in approximately 0.5 kg/week weight loss. However, many people find it difficult to maintain a calorie deficit long-term. Prescription weight loss medication can help by reducing appetite and cravings, making it easier to stick to a lower-calorie diet.
Am I eligible for prescription weight loss medication on the NHS?
You may be eligible if your BMI is 30 or above, or 27–29.9 with a weight-related health condition (diabetes, high blood pressure, sleep apnoea). Eligibility is assessed individually by your GP or a specialist weight management service. NHS access varies by region — your GP can refer you to tier 3 specialist services in your area.
What is the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist with a maximum dose of 15 mg weekly, while Wegovy (semaglutide) is a GLP-1 agonist only with a maximum of 2.4 mg weekly. Clinical trial data suggests Mounjaro may offer slightly greater average weight loss (15–21% vs ~15%), but individual results vary. Both are once-weekly injections requiring prescription and clinical assessment.
Can I get prescription weight loss medication quickly in the UK?
NHS specialist services often have waiting lists lasting months or longer, depending on your region. Private online prescribing services can assess and dispense eligible medications more quickly — typically within days. Both routes require a proper clinical assessment from a UK-licensed prescriber. Costs vary: NHS is free if eligible and available; private options range from approximately £129–£320 per month depending on dose.
Will weight loss medication stop working if I stop calorie counting?
Weight loss medications work best alongside a reduced-calorie diet and increased physical activity. If you return to previous eating patterns without calorie awareness, weight regain is likely. The medication helps control appetite and cravings, making it easier to maintain lower-calorie intake — but sustained weight management requires ongoing dietary and lifestyle commitment.
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.