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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Electrolytes and Mounjaro: What You Need to Know
When taking Mounjaro (tirzepatide) in the UK, nausea and stomach side effects are common, and dehydration is a real concern. This can affect your electrolyte balance — the minerals your body needs to function properly. Understanding how to maintain healthy electrolytes while on Mounjaro, alongside your GP's guidance, helps support your body during weight management. This guide covers what electrolytes are, why they matter on Mounjaro, and practical steps to help keep yours balanced throughout your treatment.
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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.
Electrolytes and Mounjaro: The Connection
Electrolytes are essential minerals — sodium, potassium, magnesium, and calcium — that regulate muscle function, nerve signalling, and hydration. When taking Mounjaro, side effects like nausea, vomiting, and diarrhoea can cause fluid and electrolyte loss, especially in the first few weeks at each dose increase.
Dehydration is particularly common as the medication slows stomach emptying and reduces appetite, sometimes making it harder to drink enough fluids. This electrolyte imbalance can cause fatigue, dizziness, muscle weakness, and irregular heartbeat — symptoms that might initially feel like Mounjaro side effects but could indicate you need more fluids and electrolytes.
- Sodium: Lost through sweating and vomiting; helps retain fluids
- Potassium: Critical for heart and muscle function; low levels can be serious
- Magnesium: Supports energy and muscle function; often depleted by diarrhoea
Your prescriber or GP should monitor your health regularly on Mounjaro, including checking if electrolyte problems develop.
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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.
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Practical Electrolyte Support While on Mounjaro
Start by staying hydrated — aim for 2–3 litres of water daily, though individual needs vary. Spread fluid intake throughout the day in small amounts, as large volumes can trigger nausea. Choose fluids that contain some electrolytes: coconut water, sports drinks (watch added sugars), bone broth, or electrolyte sachets you can mix into water.
Eat electrolyte-rich foods when you can tolerate them: bananas and avocados (potassium), leafy greens (magnesium), nuts and seeds, and low-sodium broths. If diarrhoea is severe or persistent, speak to your GP — they may recommend a magnesium supplement or suggest dietary changes. Never supplement potassium without medical advice, as high potassium can be dangerous. Use our free BMI calculator and GLP-1 weight loss calculator to track your overall health progress while managing Mounjaro.
- 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.
What electrolytes am I losing on Mounjaro?
Mounjaro side effects like nausea, vomiting, and diarrhoea cause losses of sodium, potassium, magnesium, and calcium. These minerals regulate muscle function, hydration, and nerve signalling. Dehydration from reduced fluid intake also depletes electrolytes. Your GP can check levels if you experience fatigue, dizziness, or muscle weakness.
How much water should I drink on Mounjaro?
Aim for 2–3 litres daily, spread throughout the day in small sips — large amounts at once can trigger nausea. Drink water with meals and between meals. If plain water causes nausea, try adding lemon or switching to electrolyte drinks, coconut water, or broths. Listen to your body and adjust based on thirst and urine colour.
Can I take electrolyte supplements while on Mounjaro?
Sodium and magnesium supplements may help if losses are significant, but never take potassium supplements without your GP's approval — high potassium levels can cause serious heart problems. Always tell your prescriber about any supplements you're considering. Food sources are usually safer than supplements.
Are electrolyte drinks safe on Mounjaro?
Yes, but choose ones low in added sugars, as high sugar intake can affect weight loss goals and blood sugar control. Sports drinks, electrolyte sachets you mix yourself, or natural options like coconut water are better choices. Avoid sugary energy drinks. Check labels and discuss with your GP if you have diabetes.
When should I contact my GP about electrolyte concerns?
Seek advice if you experience persistent dizziness, severe muscle weakness, irregular heartbeat, severe nausea lasting more than a few weeks, or prolonged diarrhoea. These may signal electrolyte imbalance or dehydration. Your GP can assess you and recommend dietary changes, supplements, or dose adjustments to Mounjaro if needed.
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.