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
Does Orlistat Work For Weight Loss?
Orlistat is a prescription weight loss medication available in the UK that works by reducing how much fat your body absorbs from food. Evidence suggests it can support modest weight loss when combined with a reduced-calorie diet and increased physical activity. On average, orlistat helps people lose around 2.5–3.5 kg more than diet and exercise alone over 12 months, though individual results vary significantly. It's been used in UK weight management for over 20 years and is available through NHS services or as a private prescription.
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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.
How Orlistat Works and What to Expect
Orlistat mechanism: Unlike GLP-1 weight loss injections (such as those used in Mounjaro or Wegovy), orlistat works locally in your digestive system rather than on your appetite centres. It blocks lipase enzymes that break down dietary fat, meaning approximately 25–30% of the fat you eat passes through your body undigested.
Expected weight loss: Clinical trials show orlistat produces average weight loss of 5–6 kg over one year when combined with a calorie-reduced diet. This is modest compared to GLP-1 medications, but it requires no injections and has a well-established safety record in the UK.
- Works best with a reduced-calorie diet (500 kcal/day deficit)
- Takes effect immediately when taken with meals
- Available on NHS for adults with BMI ≥28 with health complications, or BMI ≥30
- Available privately without waiting lists
Use our free BMI calculator above to check whether you may be eligible for NHS prescription weight loss treatment.
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.
Side Effects and Important Considerations
The most common side effects of orlistat are digestive and relate directly to how it works. Fatty stools, urgency, and oily spotting on underwear affect around 20–40% of users, particularly if you eat high-fat meals. These effects typically reduce over time as people naturally adjust their diet.
Key points for UK users: Orlistat is safe for long-term use and has no serious side effects at standard doses. However, it can reduce absorption of fat-soluble vitamins (A, D, E, K), so a multivitamin taken at a different time of day is recommended. Your GP can assess whether orlistat suits your health profile and monitor your progress through NHS weight loss programmes.
- 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 orlistat available on the NHS in the UK?
Yes. The NHS prescribes orlistat through tier 1 and tier 3 weight management services for adults with a BMI of 30 or above, or 28 or above with weight-related health conditions such as high blood pressure or type 2 diabetes. Availability and waiting times vary by region. Your GP can refer you to local services.
How does orlistat compare to GLP-1 injections like Wegovy or Mounjaro?
Orlistat and GLP-1 medications work differently. Orlistat blocks fat absorption; GLP-1 injections reduce appetite and slow digestion. GLP-1 medications typically produce greater weight loss (15–21% body weight) but are injections. Orlistat produces more modest results (3–6 kg) but has fewer side effects. Both work best with diet and exercise changes.
What are the main side effects of orlistat?
The most common side effects are digestive: fatty or oily stools, urgency to have a bowel movement, and oily spotting. These affect 20–40% of users and often improve as people adjust their diet to lower fat intake. Serious side effects are rare. Orlistat can reduce absorption of fat-soluble vitamins, so a multivitamin supplement is usually recommended.
How long does orlistat take to work?
Orlistat begins working immediately when you take it with meals—the effect is local to your digestive system. However, noticeable weight loss typically takes 2–4 weeks to become apparent and continues gradually over 12 weeks and beyond. Weight loss is most effective when combined with a reduced-calorie diet and increased physical activity.
Can I get orlistat privately in the UK without seeing my GP?
Yes. Private prescribers in the UK can assess your suitability and issue a prescription for orlistat without an NHS referral. This typically involves an online consultation. Private prescriptions cost less than GLP-1 medications (usually £20–50 per month) but require a valid clinical assessment. Always check the prescriber is GMC-registered or working under supervision.
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.