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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How Xenical Works for Weight Loss
Xenical (orlistat) is a prescription weight loss medication used to help adults in the UK manage their weight alongside diet and physical activity. Unlike newer GLP-1 weight loss injections, Xenical works through a different mechanism — it reduces the amount of fat your body absorbs from food. It's been available in the UK for over 20 years and remains an option for weight management through the NHS or private prescribing. This guide explains how Xenical works, who can use it, and how it compares to other prescription weight loss treatments available today.
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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.
How Xenical (Orlistat) Works
Xenical contains orlistat, which works in your digestive system rather than on your brain or hormones. It reduces the amount of dietary fat that your intestines absorb — approximately 25 to 30% of fat eaten. This unabsorbed fat passes through your system naturally, meaning you consume fewer calories overall.
Orlistat does not suppress appetite or affect hunger signals like GLP-1 medications such as Wegovy or Mounjaro do. Instead, it works locally in your gut, making it a different approach to weight management.
- Xenical is available as 120 mg capsules (over-the-counter strength at a UK pharmacy) or 120 mg prescription capsules taken three times daily with meals
- Most effective when combined with a reduced-calorie, lower-fat diet (the higher the fat intake, the more likely side effects occur)
- Takes approximately 24 to 48 hours to pass through your system after the last dose
- Works best for weight management uk when paired with structured lifestyle changes — diet and physical activity
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.
Xenical Eligibility and Side Effects
Who can take Xenical: Adults with a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions (high blood pressure, type 2 diabetes, abnormal cholesterol). NHS weight loss services may prescribe Xenical, though access varies by region.
Common side effects are related to fat absorption — oily spotting, urgency to use the toilet, fatty stools. These are more common with high-fat meals. Serious side effects are rare. Some oral medications (including fat-soluble vitamins and contraceptive pills) may have reduced absorption. Your GP will check for drug interactions.
Use our free BMI calculator above to check whether you may be eligible for prescription weight loss medication, then discuss options with your GP or healthcare professional.
- 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 you lose with Xenical?
Clinical trials show average weight loss of 2.7–3.2 kg over 12 weeks alongside a low-fat diet, or approximately 5–clinically studied weight loss over 6 months. Results vary significantly between individuals. Weight loss requires consistent use alongside reduced calorie intake and physical activity — Xenical is not a standalone treatment.
Is Xenical the same as Wegovy or Mounjaro?
No. Xenical (orlistat) works in your digestive system reducing fat absorption. Wegovy (semaglutide) and Mounjaro (tirzepatide) are GLP-1 injections that work on appetite hormones. GLP-1 medications typically achieve greater weight loss, but Xenical remains a valid option for weight management uk. Your prescriber will recommend the most suitable treatment.
Can you get Xenical on the NHS?
Yes, Xenical (orlistat) is available through NHS specialist weight management services, though availability and waiting times vary by region and ICB. You can also access it privately through a UK-licensed prescriber and GPhC-registered pharmacy. Your GP can advise on NHS pathways in your area.
What happens if you stop taking Xenical?
Weight loss achieved with Xenical may be regained if you stop taking it without continuing healthy eating and physical activity habits. Xenical is typically used as part of a longer-term weight management strategy, not a temporary fix. Your prescriber will discuss duration and maintenance approaches with you.
Does Xenical interact with other medications?
Yes. Orlistat reduces absorption of fat-soluble vitamins (A, D, E, K) and some oral medications including oral contraceptives. If you take any regular medication, inform your GP or prescriber before starting Xenical. Vitamins may need to be taken at a different time, and backup contraception may be needed.
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.