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
How Does Orlistat Work for Weight Loss?
Orlistat is a prescription weight loss medication available in the UK that works differently to injection-based treatments. It's a lipase inhibitor that reduces how much dietary fat your body absorbs, helping you lose weight when combined with a reduced-calorie diet. This guide explains how orlistat works, who is eligible, and how NHS weight management in the UK compares to other prescription options available today.
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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 Prescription Weight Loss Options and How They Compare
Orlistat is one of several prescription weight loss medications available in the UK. It works by blocking pancreatic lipase, an enzyme that breaks down dietary fat in your digestive system. This means approximately 25–30% of the fat you eat is not absorbed and is instead passed through your body, reducing overall calorie intake.
- Orlistat (Xenical, Alli): Lipase inhibitor — blocks fat absorption. Requires reduced-calorie diet (around 120g fat per day).
- GLP-1 medications (Wegovy, Saxenda): Appetite suppressants — reduce hunger and food cravings. Available on NHS through specialist services or privately.
- Mounjaro (tirzepatide): Dual GIP/GLP-1 agonist — may help suppress appetite more powerfully. NICE-approved for NHS specialist weight management services.
Unlike GLP-1 injections, orlistat is an oral medication taken three times daily with meals. All prescription weight loss medications in the UK require a clinical assessment and medical supervision.
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 and Private Prescription Routes in the UK
In the UK, prescription weight loss medications are accessed through two main routes. NHS weight management is delivered through specialist tier 3 services — your GP can refer you if you meet eligibility criteria (BMI 30 or above, or 27–29.9 with weight-related conditions). NHS access varies significantly by region, and waiting lists can be lengthy.
Private prescription is available through UK-licensed prescribers and GPhC-registered pharmacies for all three main options: orlistat, GLP-1 medications, and Mounjaro. Private assessment can be faster, though medication costs apply. Whatever route you choose, speak with your GP first — they can advise on your individual health status, medication interactions, and best options for sustainable weight loss alongside 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.
How much weight can I expect to lose with orlistat?
Clinical trials show orlistat helps achieve an average weight loss of 2.5–3.5 kg more than diet alone over 6–12 months. Individual results vary significantly. For best results, combine orlistat with a reduced-calorie diet (around 120g fat daily) and increased physical activity. Use our free GLP-1 weight loss calculator to compare projected outcomes across different prescription options.
What are the main side effects of orlistat?
Common side effects include oily spotting, urgent bowel movements, and fatty stools — especially if you eat high-fat foods. These effects reduce as you adjust your diet to lower fat intake. Serious side effects are rare but can include liver problems. Always inform your GP of any persistent side effects.
Can I get orlistat on the NHS in the UK?
Yes, orlistat is available on the NHS through your GP or specialist weight management services for eligible adults. You must have a BMI of 30 or above (or 27 if you have weight-related health conditions), have tried lifestyle changes, and be committed to dietary support. Your GP can discuss whether it's appropriate for you.
How does orlistat compare to GLP-1 injections like Wegovy?
Orlistat blocks fat absorption; GLP-1 injections suppress appetite. GLP-1 medications (Mounjaro, Wegovy) typically produce greater average weight loss (15–21%) than orlistat. However, GLP-1 injections are weekly injections, whereas orlistat is taken three times daily by mouth. Both require prescription and clinical assessment — your GP can discuss which suits your health profile best.
Do I need to follow a special diet while taking orlistat?
Yes — orlistat works best with a low-fat diet (around 120g fat per day or less). Without dietary change, side effects may be bothersome and weight loss minimal. Combine orlistat with a reduced-calorie diet and increased physical activity for best results. Our free progress tracker can help you log dietary and weight changes over time.
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.