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
Alli Weight Loss Supplement and UK Prescription Alternatives
Alli (orlistat) is an over-the-counter weight loss supplement available in UK pharmacies, but if you're looking for prescription weight management options, several more effective alternatives are now available through the NHS and private prescribing. This guide explains how prescription weight management medications work, who is eligible, and how to access them in the UK.
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 Management Options
If you have a BMI of 30 or above (or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea), you may be eligible for prescription weight management medication. The three UK-licensed options are:
- Mounjaro (tirzepatide) — A dual GIP/GLP-1 receptor agonist injected once weekly. Clinical trials showed average weight loss of approximately 15–21% of body weight over 72 weeks, though individual results vary.
- Wegovy (semaglutide) — A GLP-1 receptor agonist injected once weekly. Average weight loss in clinical trials was approximately 14.9% of body weight at 68 weeks alongside a reduced-calorie diet and increased physical activity.
- Saxenda (liraglutide) — A daily GLP-1 injection. Evidence supports modest weight loss, though less extensively studied than Mounjaro and Wegovy.
Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses. All three medications are prescription-only and require clinical assessment before being prescribed.
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.
Accessing Prescription Weight Management in the UK
You can access prescription weight management through two routes: NHS specialist services or private prescribing. NHS access is through tier 3 specialist weight management services — your GP can refer you, though waiting times vary significantly by region and can be several months. Private access is available through GPhC-registered online prescribing services, which require a brief clinical assessment and typically cost £129–£320 per month depending on dose.
Whichever route you choose, these medications work best alongside a reduced-calorie diet and increased physical activity. Use our free BMI calculator to check your personal BMI and assess your eligibility, then have a conversation with your GP about whether prescription weight management 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.
What is the difference between Alli and prescription weight loss injections?
Alli (orlistat) is an over-the-counter supplement that reduces fat absorption in the digestive system. Prescription GLP-1 medications like Mounjaro and Wegovy work differently — they act on appetite regulation in the brain and are significantly more effective. Prescription options typically result in 15–clinically studied weight loss versus 3–5% with Alli.
Who is eligible for prescription weight management in the UK?
Adults with a BMI of 30 or above, or 27–29.9 with at least one weight-related health condition (type 2 diabetes, prediabetes, high blood pressure, sleep apnoea, or cardiovascular disease) may be eligible. South Asian, Chinese, Black African, or Black Caribbean adults have slightly lower thresholds. Your GP or a licensed prescriber can assess your individual eligibility.
Can I get GLP-1 medication like Mounjaro through the NHS?
Yes, Mounjaro and other GLP-1 medications are available through NHS specialist tier 3 weight management services. You typically need a GP referral. Availability and waiting times vary significantly by region. Private access is also available through GPhC-registered prescribers without an NHS referral.
How much weight can I expect to lose with Mounjaro or Wegovy?
Clinical trials showed average weight loss of 15–21% of body weight with Mounjaro and approximately 15% with Wegovy over 18–24 months, but individual results vary significantly. Some people lose more, some less. Weight loss depends on adherence to a reduced-calorie diet, increased physical activity, and individual metabolism. Use our weight loss calculator for a personalised estimate.
Are prescription weight loss injections available on the NHS in all areas?
No. Availability varies significantly by region because each NHS Integrated Care Board (ICB) sets its own funding and referral criteria. Some areas have good access; others have long waiting lists or limited funding. Ask your GP about availability in your area, or consider private prescribing as an alternative if NHS access is limited.
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.