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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Water Pills And Weight Loss — UK Health Information
Water pills (diuretics) can cause temporary weight loss by reducing fluid retention, but this is not true fat loss and the weight returns when you stop taking them. If you're looking for sustainable weight management in the UK, there are more effective approaches — including prescription weight loss medication and lifestyle changes. This guide explains how water pills work, their limitations, and evidence-based alternatives for lasting results.
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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 Water Pills Affect Weight And Fluid Retention
Water pills (diuretics) work by increasing urine output, which temporarily reduces the amount of fluid your body retains. This can cause gradual weight management on the scales — sometimes 1–2 kg in just a few days. However, this is fluid loss, not fat loss. Once you stop taking water pills, your body rehydrates and the weight returns almost immediately.
- Prescription diuretics are used medically for conditions like high blood pressure and heart failure — not for weight loss
- Over-the-counter diuretics (including herbal diuretics) can cause dehydration, electrolyte imbalances, and dizziness
- Using water pills for cosmetic weight loss is ineffective and potentially unsafe
- The NHS does not recommend diuretics for weight management
For sustainable weight loss in the UK, the focus should be on reducing body fat through calorie deficit and lifestyle changes.
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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.
Evidence-Based Alternatives To Water Pills For Weight Loss
If you're seeking genuine, sustainable weight loss, several approaches are recommended by the NHS and supported by clinical evidence. Calorie deficit — reducing food intake by approximately 500 kcal per day — typically results in safe weight loss of 0.5–1 kg per week. Regular physical activity, reduced alcohol consumption, and improved sleep quality all support weight management.
For adults with a BMI of 30 or above, or 27 or above with weight-related health conditions, prescription weight loss medications may be appropriate. These include GLP-1 injections like Wegovy (semaglutide), which clinical trials showed helped participants lose an average of around 15% of their body weight. Check your BMI using our free BMI calculator to see if you may be eligible, and discuss weight management options with your GP.
- 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 you lose real weight with water pills?
No. Water pills cause temporary fluid loss only. The weight loss is not fat loss and returns within days of stopping them. For real, lasting weight loss, you need to reduce calorie intake and increase physical activity. If you're eligible, prescription weight loss medication alongside lifestyle changes is evidence-based and more effective.
Are water pills safe for weight loss?
Water pills are not recommended for weight loss. When used for non-medical reasons, they can cause dehydration, electrolyte imbalances, dizziness, and muscle weakness. Prescription diuretics are only for specific medical conditions like high blood pressure. Never use them for cosmetic weight loss without medical supervision.
What does the NHS say about diuretics and weight management?
The NHS does not recommend diuretics for weight loss. Weight loss should be achieved through sustainable calorie deficit and increased physical activity. For adults meeting NHS criteria (BMI ≥30 or ≥27 with comorbidities), prescription weight loss medication like GLP-1 injections may be appropriate following clinical assessment by your GP.
What's more effective than water pills for losing weight?
Calorie deficit (around 500 kcal/day less) supports steady weight loss of 0.5–1 kg per week. Regular exercise, reduced alcohol, and better sleep help. For eligible adults, prescription weight loss injections like Wegovy are clinically proven to support significant weight loss alongside lifestyle changes. Our GLP-1 weight loss calculator can help estimate potential results.
How do I know if I'm eligible for prescription weight loss medication?
Adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions (like type 2 diabetes or high blood pressure), may be eligible. Use our free BMI calculator to check your BMI, then speak with your GP about weight management options available through the NHS or private prescription services.
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.