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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Fibre Supplements For Weight Loss: What Works In The UK
Fibre supplements are popular for weight management in the UK, but they work differently to prescription weight loss medication. Whilst soluble fibre can help you feel fuller for longer, the evidence for significant weight loss is modest. For adults struggling with excess weight, prescription options like Mounjaro and Wegovy may offer more substantial results when used alongside lifestyle changes. This guide explores how fibre fits into weight management and what NHS-approved prescription alternatives are available if you're eligible.
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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 Loss Options Available In The UK
For adults seeking weight management support in the UK, prescription medications offer evidence-based alternatives to supplements. Mounjaro (tirzepatide) and Wegovy (semaglutide) are GLP-1 receptor agonist medications licensed for weight loss in the UK, with clinical trial data showing average weight loss of 15–21% body weight. Saxenda (liraglutide) is another option.
- Mounjaro: Dual GIP and GLP-1 agonist, once-weekly injection, doses from 2.5 mg to 15 mg
- Wegovy: GLP-1 agonist, once-weekly injection, doses from 0.25 mg to 2.4 mg
- Saxenda: GLP-1 agonist, once-daily injection, doses from 0.6 mg to 3 mg
All three are prescription-only medicines available to eligible adults through NHS specialist services or private prescribing. Try our free GLP-1 weight loss calculator to see projected results at different doses. Unlike fibre supplements, these medications work by affecting appetite hormones and are supported by extensive clinical evidence for significant weight management results.
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 Eligibility And How To Access Prescription Weight Loss Support
In the UK, prescription weight loss medications are available to adults with a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults due to higher health risks at lower BMI levels.
NHS access: Referral to a tier 3 specialist weight management service from your GP. Waiting times vary by region.
Private access: Online consultation with a UK-licensed prescriber, no NHS referral needed. Check your BMI using our free BMI calculator above, then speak with your GP or a private prescriber about whether prescription weight loss medication is right for you. Unlike unregulated supplements, prescription medications have undergone rigorous clinical trials and come with professional medical support.
- 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.
Can fibre supplements alone help me lose weight?
Fibre supplements can support weight loss by promoting fullness and improving digestion, but evidence for significant weight loss is limited. A typical fibre supplement might contribute to modest weight loss (around 1–2 kg over several weeks) when combined with a calorie deficit. For more substantial results, prescription weight loss medications like Mounjaro or Wegovy show clinical evidence of 15–21% average body weight loss.
What is the difference between fibre supplements and prescription weight loss medication?
Fibre supplements work mechanically by adding bulk to food and slowing digestion. Prescription weight loss medications like Wegovy and Mounjaro are GLP-1 agonists that work on appetite hormones in the brain, affecting hunger signals, fullness, and food cravings. Prescription medications have robust clinical trial evidence and require medical assessment, whilst fibre supplements are dietary products available over the counter.
Am I eligible for prescription weight loss medication on the NHS?
You may be eligible if you have a BMI of 30 or above, or 27–29.9 with a weight-related health condition like diabetes or high blood pressure. Lower thresholds apply for certain ethnic groups. Eligibility is assessed by your GP or a specialist weight management service. Speak with your GP about referral to tier 3 services, or consider a private online consultation with a UK-licensed prescriber.
What is the most effective prescription weight loss medication in the UK?
Clinical trial evidence suggests Mounjaro (tirzepatide) may offer slightly higher average weight loss (up to 21%) compared to Wegovy (around 15%), but individual results vary significantly. Both are prescription-only and require clinical assessment to determine suitability. Your prescriber will consider your health profile, previous responses to medication, and personal circumstances when recommending the best option for you.
Can I combine fibre supplements with prescription weight loss medication?
Fibre supplements and prescription weight loss medications work through different mechanisms and can theoretically be used together. However, this should only be done under medical supervision. GLP-1 medications already slow gastric emptying, so adding extra fibre could cause digestive discomfort. Always discuss any supplements or dietary changes with your prescriber or GP before starting them alongside prescription weight loss treatment.
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.