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
Do Laxatives Actually Cause Weight Loss?
Laxatives do not cause genuine weight loss, though they may temporarily reduce the number on the scales. Any weight drop is due to water and stool loss, not fat loss, and returns within days of stopping. For sustainable weight management in the UK, evidence-based approaches like dietary changes, physical activity, and prescription weight loss medication are far more effective and safer. Understanding the difference between water weight and actual fat loss is crucial when considering your health options.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Laxatives Affect Your Weight
When you take a laxative, it stimulates bowel movements and increases water content in your stool, leading to rapid fluid loss. This can create a temporary drop in weight within hours — often 1–3 kg (2–7 lbs) — which might seem encouraging on the scales. However, this is not fat loss. Your body regains this water weight once you hydrate normally, usually within 24–48 hours.
The problem intensifies if laxatives are misused regularly. Chronic laxative use can lead to dehydration, electrolyte imbalances, and dependency — your bowel may stop functioning normally without them. This is why laxatives are not a weight loss strategy recognised by the NHS or recommended by GPs for weight management purposes.
- Weight loss from laxatives is temporary water loss, not fat loss
- Regular misuse can damage digestive health and cause dependency
- The NHS does not recommend laxatives for weight loss
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.
Safe and Effective Weight Loss Alternatives
For genuine, sustainable weight loss in the UK, the NHS recommends a calorie deficit achieved through balanced eating and increased physical activity. Aim for a loss of 0.5–1 kg (1–2 lbs) per week, which is safe and maintainable. Our free BMI calculator can help you understand your current weight status and set realistic goals.
If you have a BMI of 30 or above, or 27+ with weight-related health conditions, you may be eligible for prescription weight loss medication through NHS specialist weight management services or private prescribing. Our GLP-1 weight loss calculator can help you explore potential outcomes with evidence-based medications like semaglutide. These work through appetite regulation — not fluid loss — and support genuine fat loss when combined with lifestyle changes.
- 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.
Why do laxatives make you lose weight so quickly?
Laxatives cause rapid water and stool loss, not fat loss. The temporary weight drop is due to dehydration and bowel emptying. This weight returns within 24–48 hours once you rehydrate normally. It's why laxative-induced weight loss is not genuine or sustainable.
Can regular laxative use help with long-term weight loss?
No. Regular laxative use does not support long-term weight loss and can cause serious health problems including dehydration, electrolyte imbalances, and bowel dependency. The NHS does not recommend laxatives for weight management. Speak to your GP about safe alternatives.
What's the difference between water weight and fat loss?
Water weight is temporary fluid loss that returns quickly with hydration. Fat loss involves burning stored fat through a sustained calorie deficit — this takes weeks but is permanent. Genuine weight loss requires fat loss, not just water loss. Use our free weight converter to track progress in familiar units like stone and pounds.
Are there prescription weight loss options available in the UK?
Yes. If you meet eligibility criteria (BMI 30+ or BMI 27+ with weight-related health conditions), you may access prescription weight loss medication through NHS specialist services or private prescribing. These medications work alongside diet and exercise to support sustainable fat loss over time.
How much weight should I aim to lose per week safely?
The NHS recommends losing 0.5–1 kg (1–2 lbs) per week for safe, sustainable weight loss. This pace helps preserve muscle mass and is more likely to become a lasting lifestyle change. Faster weight loss often includes muscle and water loss alongside fat — not ideal. Your GP can advise on your personal targets.
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.