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
Drinking Water on Mounjaro — Why Hydration Matters
Staying properly hydrated is especially important when taking Mounjaro (tirzepatide), as nausea, vomiting, and constipation are common side effects that increase fluid loss. Water helps manage these digestive symptoms, supports kidney function, and improves overall tolerance of the medication. The NHS recommends around 6 to 8 glasses of fluid daily for adults, but Mounjaro users may benefit from slightly more. This guide explains why hydration matters on tirzepatide, how much water to aim for, and practical strategies to maintain adequate fluid intake while managing common side effects.
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.
Hydration on Mounjaro — How Much Water to Drink
There is no single "correct" water intake — it varies by age, activity level, climate, and individual health. However, the NHS recommends 6 to 8 glasses of fluid daily (about 1.5 to 2 litres) for most UK adults. People taking Mounjaro may benefit from increasing this slightly, particularly if experiencing nausea, diarrhoea, or vomiting, as these side effects cause fluid loss.
Practical hydration targets while on tirzepatide:
- Aim for 2 to 2.5 litres of fluid daily (or more in hot weather or during exercise)
- Drink water gradually throughout the day — not large amounts at once, which can worsen nausea
- Sip water with meals or shortly after, as Mounjaro slows gastric emptying
- Monitor urine colour — pale yellow indicates good hydration; dark yellow suggests you need more fluids
- Avoid sugary drinks and excessive caffeine, which can worsen dehydration
If you experience severe vomiting or persistent diarrhoea, you may need additional fluids — discuss with your GP or prescriber.
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.
Why Water Helps Manage Mounjaro Side Effects
Nausea, constipation, and diarrhoea are among the most common side effects reported in Mounjaro clinical trials. Adequate hydration helps address each: water eases constipation by softening stool, reduces nausea by preventing dehydration, and replaces fluids lost through diarrhoea. Dehydration can amplify nausea and fatigue, making side effects feel worse. Staying hydrated also supports your kidneys and overall metabolic health as your body adjusts to tirzepatide.
Small, frequent sips of water are often better tolerated than large amounts at once. Some users find room-temperature or warm water easier on the stomach than cold water. If nausea is severe or persists beyond the first few weeks, inform your prescriber — they may adjust your Mounjaro dose or suggest additional strategies.
- 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.
How much water should I drink while taking Mounjaro?
Aim for 2 to 2.5 litres (roughly 8 to 10 glasses) of fluid daily, or more if you exercise or live in a hot climate. Drink gradually throughout the day rather than large amounts at once. The NHS recommends 6 to 8 glasses for adults generally, but Mounjaro users benefit from slightly more due to common side effects like nausea and diarrhoea.
Can drinking too much water on Mounjaro cause problems?
Excessive water intake is uncommon, but very large amounts (several litres in a short time) can be uncomfortable and may worsen nausea. Drink water steadily throughout the day. If you experience persistent severe nausea, vomiting, or swelling, contact your GP immediately — these could indicate a serious issue unrelated to hydration.
Does Mounjaro cause dehydration?
Mounjaro itself does not directly cause dehydration, but common side effects like vomiting and diarrhoea increase fluid loss. This is why staying hydrated is important. Monitor your urine colour — pale yellow indicates good hydration. If you experience severe or persistent vomiting, speak to your prescriber about whether you need additional support.
What's the best type of fluid to drink on Mounjaro?
Water is ideal. Herbal tea, milk, and clear broths also count toward your fluid intake. Avoid sugary drinks, excessive caffeine, and alcohol, which can worsen dehydration and nausea. Some users find electrolyte drinks helpful if experiencing significant diarrhoea or vomiting, but discuss this with your GP first.
Should I drink water at specific times when taking Mounjaro?
No strict timing is required, but sipping water with or shortly after meals often works well. Since Mounjaro slows how quickly food leaves your stomach, spreading water intake evenly throughout the day is gentler than drinking large amounts at once. Small, frequent sips are usually better tolerated than gulping water when nausea is present.
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.