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
Colonics and Weight Loss — What UK Evidence Shows
Colonics (colonic irrigation) are sometimes promoted for weight loss and health, but there is no strong clinical evidence that they support sustainable weight reduction. If you're looking to lose weight in the UK, prescription medications and lifestyle changes are evidence-based alternatives. This guide explains NHS-approved weight management options, eligibility criteria, and how to discuss options with your GP.
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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.
Prescription Weight Management Options in the UK
The UK has several prescription weight loss medications licensed for adults with excess weight. These are supported by clinical evidence and available through NHS specialist services or private prescribing following a clinical assessment.
- Mounjaro (tirzepatide) — once-weekly injection. Dual GIP and GLP-1 receptor agonist. Clinical trials showed average weight loss of 15–21% body weight alongside a reduced-calorie diet and increased physical activity.
- Wegovy (semaglutide) — once-weekly injection. GLP-1 receptor agonist. Average weight loss approximately 15% body weight in clinical trials.
- Saxenda (liraglutide) — once-daily injection. GLP-1 receptor agonist. Longer-established option with proven safety record.
All three are prescription-only and require a clinical assessment by a licensed prescriber to confirm suitability. Unlike unproven remedies, these medications work by helping regulate appetite and support feeling fuller after smaller meals.
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 — How to Get Started
NHS access: Referral to a tier 3 specialist weight management service through your GP. Availability and waiting times vary significantly by region (ICB). NHS typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or sleep apnoea.
Private access: Online consultation with a UK-licensed prescriber, prescription issued if clinically appropriate, dispensed by a GPhC-registered pharmacy. No NHS referral needed. Available immediately for eligible adults.
Start by discussing weight management options with your GP. They can assess your individual health, explain eligibility, and support whichever route is most appropriate for you. Use our free BMI calculator to check your starting point, and our GLP-1 weight loss calculator to understand potential outcomes at different doses.
- 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.
Are colonics effective for weight loss?
No strong clinical evidence supports colonics for sustainable weight loss. Any weight loss is typically temporary fluid loss. Prescription medications like Mounjaro and Wegovy are evidence-based alternatives supported by clinical trials. Speak to your GP about medically-supervised weight management options.
Who is eligible for prescription weight loss medication in the UK?
Adults with a BMI of 30 or above, or 27–29.9 with weight-related conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Adults of South Asian, Chinese, Black African, or Caribbean heritage may qualify at lower BMI thresholds. Your GP or prescriber will assess individual eligibility.
What is the difference between Mounjaro and Wegovy?
Both are once-weekly injections for weight management in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist with average weight loss of 15–21% body weight. Wegovy (semaglutide) is a single GLP-1 agonist with average weight loss around 15%. Individual results vary. Your prescriber will recommend the most suitable option.
How quickly will I lose weight on prescription medication?
Weight loss varies individually. Safe, sustainable loss is typically 0.5–1 kg per week. Prescription medications work alongside a reduced-calorie diet and increased physical activity—not instead of lifestyle changes. Results are not assured. Our progress tracker can help you monitor your journey.
Can I access weight loss medication through the NHS?
Yes, through NHS specialist tier 3 weight management services. Your GP can refer you. NHS availability varies by region and waiting times can be several months to years in some areas. Private prescribing offers faster access following an online clinical assessment with a UK-licensed prescriber.
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.