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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Can You Take Magnesium With Mounjaro?
If you're taking Mounjaro (tirzepatide) for weight management, you may be wondering whether it's safe to take magnesium supplements alongside it. Magnesium is an essential mineral involved in hundreds of bodily functions, and some people on weight loss medication experience changes in nutrient absorption or digestive symptoms that may affect their magnesium levels. This guide explains the relationship between magnesium and Mounjaro, what you need to know, and when to speak with your GP or prescriber.
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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.
How Mounjaro May Affect Magnesium and Nutrient Absorption
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist that slows gastric emptying — how quickly food leaves your stomach. This can affect how your digestive system absorbs nutrients, including magnesium. Additionally, some people taking Mounjaro experience constipation or diarrhoea, both of which can impact mineral absorption and electrolyte balance.
Magnesium absorption may be reduced if you have:
- Persistent diarrhoea (increases magnesium loss)
- Severe constipation (reduces absorption time)
- Reduced appetite leading to insufficient dietary magnesium intake
- Changes in stomach acid levels
If you're on a reduced-calorie diet while taking Mounjaro, you may also be consuming less magnesium from food sources. Your GP can check your magnesium levels with a blood test if you have symptoms like muscle weakness, fatigue, or irregular heartbeat.
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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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Taking Magnesium Supplements With Mounjaro — Safety Guidance
Magnesium supplements are generally considered safe to take alongside Mounjaro, but timing and type matter. Magnesium may reduce absorption of oral medications if taken at the same time, so space supplements at least 2 hours away from your Mounjaro injection or other medications. Take magnesium at a consistent time daily — morning or evening — but not immediately before or after eating if you have severe nausea.
Forms like magnesium citrate or glycinate are often better tolerated than magnesium oxide, which can worsen constipation or diarrhoea. Always check with your prescriber before starting any supplement, especially if you're managing blood sugar or taking other medications. Never exceed the recommended daily allowance (RDA: 400mg for adult men, 310mg for adult women) without medical guidance.
- 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.
Will Mounjaro cause magnesium deficiency?
Mounjaro itself doesn't directly cause deficiency, but it may reduce magnesium absorption through digestive changes and reduced appetite. If you experience constipation or diarrhoea on Mounjaro, or if you're eating significantly less, your magnesium intake may drop. Speak to your GP if you have symptoms like fatigue, muscle cramps, or irregular heartbeat — they can test your magnesium levels.
Can I take magnesium tablets with Mounjaro injections?
Yes, magnesium supplements are generally safe with Mounjaro. However, space them at least 2 hours apart from your weekly injection and other medications, as magnesium can reduce absorption of oral drugs. Consistency matters — take your supplement at the same time each day. Always inform your prescriber of all supplements you're taking.
Which type of magnesium is best while on Mounjaro?
Magnesium citrate or glycinate are often better tolerated than magnesium oxide, especially if you're experiencing digestive side effects from Mounjaro. Oxide can worsen constipation or diarrhoea. Check the product label and discuss with your GP or pharmacist which form suits your individual symptoms and needs best.
Should I take magnesium if I have diarrhoea from Mounjaro?
If Mounjaro-related diarrhoea is causing magnesium loss, supplementation may help — but only under GP guidance. Diarrhoea increases magnesium excretion, so some people do benefit from supplements. However, the underlying diarrhoea should be managed first. Your prescriber can advise whether a dose adjustment or magnesium supplement is right for you.
What magnesium dose is safe on Mounjaro?
The UK RDA is 400mg daily for men and 310mg for women. Do not exceed this without medical supervision. Most magnesium supplements provide 150–400mg per dose. Start low and assess tolerance, especially if you have GI symptoms. Always consult your GP or the supplement's guidance before starting — your individual needs may differ based on diet and digestive health.
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