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 — UK Reviews and How They Compare
Alli (orlistat 60 mg) is an over-the-counter weight loss tablet available in the UK without a prescription. It works by reducing how much fat your body absorbs from food. Many UK adults have tried Alli, and reviews are mixed — some find modest results helpful, while others report limited effectiveness. This guide explains how Alli works, what to expect, and how it compares to prescription weight loss alternatives available through the NHS or private weight management services.
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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.
How Alli Works and What the Evidence Shows
Alli contains orlistat 60 mg, a lipase inhibitor that blocks around 30% of dietary fat absorption in your gut. This unabsorbed fat is then excreted, which means you absorb fewer calories from fatty foods. The mechanism is straightforward but requires strict dietary discipline to be effective.
Evidence for Alli's effectiveness is modest. Clinical trials show average weight loss of around 2–3 kg over 6 months when combined with a calorie-reduced diet — roughly 0.5 kg more than diet alone. This is much lower than prescription weight loss medications. Common side effects include oily stools, urgent bowel movements, and fatty stools, particularly if you eat high-fat meals. UK adults often report these gastrointestinal effects make it difficult to stick with long-term.
Alli requires you to follow a low-fat diet (less than 15 grams fat per meal) for it to work effectively. Without dietary changes, Alli offers minimal benefit. It is available without prescription from pharmacies and supermarkets in the UK, making it an accessible first option for some people.
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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.
Alli vs Prescription Weight Loss Options in the UK
If you've tried over-the-counter tablets like Alli with limited success, prescription weight loss medications are significantly more effective. GLP-1 medications like Wegovy (semaglutide) help you manage appetite directly through a different mechanism — activating natural hormone pathways that signal fullness to your brain. Clinical trials show average weight loss of around 14–15% of body weight over several months, far exceeding Alli's results.
Prescription options are available through the NHS (via specialist tier 3 weight management services) or privately through online consultations with UK-licensed prescribers. Use our free GLP-1 weight loss calculator to estimate potential weight loss with prescription alternatives. Our BMI calculator can also help determine whether you may be eligible for prescription weight management support.
Sustainable weight loss combines medication (if appropriate), dietary changes, and increased physical activity. The NHS recommends losing weight at a rate of 0.5–1 kg per week. Track your progress using our free progress tracker, and discuss options with your GP to find what works best for your situation.
- 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 effective for weight loss UK?
Alli shows modest results — clinical trials show average weight loss of 2–3 kg over 6 months with diet, roughly 0.5 kg more than diet alone. It requires strict low-fat eating to be effective. Results vary significantly between individuals, and many UK adults find the gastrointestinal side effects make it difficult to sustain long-term.
What are the side effects of Alli weight loss tablets?
Common side effects include oily stools, urgent bowel movements, fatty stools, and urgency to use the toilet — especially after eating fatty meals. These occur because unabsorbed fat passes through your digestive system. Effects are more pronounced if you eat high-fat foods, which is why a low-fat diet is essential.
Can I get Alli on the NHS?
Alli (orlistat 60 mg) is available over-the-counter without prescription from UK pharmacies and supermarkets. Higher-dose orlistat (120 mg) is available on NHS prescription for people with BMI 30 or above, but access varies by region. Speak to your GP about prescription options if you qualify.
How does Alli compare to Wegovy or Mounjaro?
Alli achieves average weight loss of 2–3 kg; Wegovy and Mounjaro achieve 14–clinically studied weight loss in clinical trials. Prescription medications work through appetite regulation rather than fat blocking. Alli requires no prescription but is much less effective. Prescription options require clinical assessment and are available through NHS specialist services or privately.
How long does Alli take to work?
Alli typically shows results within 2–4 weeks if combined with a reduced-calorie diet. However, weight loss is gradual. Most clinical benefit appears over 3–6 months. Individual results vary, and sustained effects depend on maintaining low-fat eating habits and calorie deficit alongside the tablet.
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.