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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Alli Weight Loss Tablets and Prescription Alternatives in the UK
Alli (orlistat) is an over-the-counter weight loss tablet available in UK pharmacies without a prescription. However, if you're looking for stronger prescription weight management options, several licensed medications are available in the UK for eligible adults. These prescription alternatives — including Mounjaro, Wegovy, and Saxenda — work differently and may offer greater support for weight loss uk alongside lifestyle changes. This guide explains what's available and how to find out if you qualify.
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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
If you're interested in prescription weight loss medication, three options are currently licensed in the UK for eligible adults:
- Mounjaro (tirzepatide) — a once-weekly injection that activates dual GIP and GLP-1 pathways. Clinical trials showed average weight loss of 15–21% of body weight at the highest dose.
- Wegovy (semaglutide) — a once-weekly GLP-1 injection. In clinical trials, participants lost an average of approximately 15% of their body weight.
- Saxenda (liraglutide) — a daily GLP-1 injection. Approved for weight management in adults with a BMI of 30 or above, or 27+ with weight-related health conditions.
All three are prescription-only medicines requiring a clinical assessment. Individual results vary significantly, and these medications work best alongside a reduced-calorie diet and increased physical activity. Use our free GLP-1 weight loss calculator above to explore potential outcomes at different doses.
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 to Prescription Weight Loss
NHS route: Prescription weight loss medications are available through NHS weight loss specialist tier 3/4 weight management services. You'll need a GP referral, and access varies significantly by region. Waiting lists can be lengthy in many areas.
Private route: Available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. No NHS referral needed, but you'll pay for the medication directly. Costs vary by dose and provider.
To find out if you're eligible, calculate your BMI using our free BMI calculator above. Adults with a BMI of 30 or above, or 27–29.9 with weight-related conditions, may qualify. Speak with your GP about which option suits you best.
- 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.
Is Alli available on the NHS?
Alli (orlistat) is available over-the-counter from UK pharmacies without prescription. Some NHS areas may provide orlistat through primary care for eligible patients, but prescription-only alternatives like Mounjaro and Wegovy may be more effective for significant weight management uk.
What's the difference between Alli and prescription weight loss injections?
Alli works by reducing fat absorption in the digestive system. GLP-1 injections like Wegovy work by reducing appetite and supporting fullness. Prescription medications typically show greater average weight loss in clinical trials and require clinical assessment.
How do I get Mounjaro or Wegovy on the NHS?
Ask your GP for a referral to your local tier 3 weight management service. They'll assess your eligibility based on your BMI and health conditions. Availability varies by region, and waiting times can be several months. Private prescribing is also available without NHS referral.
Are prescription weight loss injections suitable for everyone?
No. You'll need a clinical assessment to ensure they're safe for you. They're not suitable during pregnancy, for people under 18, or those with certain medical conditions like severe gastroparesis. Your prescriber will review your full health history.
How much weight can I expect to lose with GLP-1 medication?
Clinical trials show average weight loss of 15–21% of body weight, depending on the medication and dose. However, individual results vary significantly. Results are best achieved alongside a reduced-calorie diet and increased physical activity. Use our weight loss calculator to estimate potential outcomes.
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.