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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Supplements to take on Mounjaro — what's safe and what to avoid
If you're taking Mounjaro (tirzepatide) for weight management, you may be wondering which supplements are safe to use alongside it. Because Mounjaro slows how quickly food leaves your stomach, it can affect nutrient absorption and increase the need for certain vitamins and minerals. This guide covers the supplements that may support your health while on Mounjaro, which ones to avoid, and when to discuss supplementation with your GP. Always consult your healthcare professional before starting any new supplement — even though many are available over the counter, they can interact with prescription medications.
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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.
Common supplements to consider whilst on Mounjaro
Several supplements may be worth considering if you're on Mounjaro, particularly because the medication slows gastric emptying (how quickly food passes through your stomach), which can affect nutrient absorption over time:
- B vitamins — B12, B6, and folate are often depleted with prolonged use of medications that affect stomach acid. A B-complex supplement may help, particularly if you're experiencing fatigue.
- Vitamin D — Many UK adults are deficient, especially during winter months. Mounjaro doesn't directly deplete vitamin D, but adequate levels support bone health and immune function.
- Iron — If you're experiencing persistent tiredness, your GP may check your iron levels. Iron absorption is affected by stomach acid changes, so supplementation may be recommended.
- Calcium — Reduced stomach acid can affect calcium absorption. If you don't consume enough dairy or fortified plant-based alternatives, a supplement may be suggested.
- Electrolytes — If you experience nausea, vomiting, or diarrhoea (common side effects), electrolyte balance becomes important. Your GP can advise whether a supplement is needed.
Use our GLP-1 weight loss calculator to track how your weight management is progressing alongside any lifestyle and supplement adjustments you make.
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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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Supplements to avoid or use with caution on Mounjaro
Some supplements can interact with Mounjaro or reduce its effectiveness. Avoid or discuss these with your GP before taking:
- High-dose mineral supplements — Excessive zinc, magnesium, or other minerals can interfere with medication absorption. Stick to recommended daily amounts.
- Herbal appetite stimulants — Supplements marketed to increase appetite (like fenugreek or maca) work against Mounjaro's mechanism and should be avoided.
- Fat-soluble vitamin supplements in excess — Vitamins A, D, E, and K are stored in body fat; excessive amounts can accumulate. Stick to the recommended dietary allowance.
- Certain oral contraceptives — Not a supplement, but oral birth control medications are less effective with Mounjaro; discuss alternatives with your GP.
Your GP or prescriber should always be informed of any supplements you're taking to identify potential interactions and ensure your treatment plan is optimised.
- 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 I take a standard multivitamin whilst on Mounjaro?
Yes, a standard multivitamin is generally safe with Mounjaro in most cases. However, because Mounjaro affects nutrient absorption, inform your GP about any multivitamins you take. Your prescriber may recommend specific vitamins (like B12 or vitamin D) depending on your individual health and side effects. Avoid mega-dose multivitamins and stick to products meeting the recommended daily allowance (RDA).
Should I take supplements if I'm not experiencing side effects?
Not necessarily. If you're eating a balanced diet and feeling well, you may not need supplements. However, if you experience fatigue, hair loss (alopecia), or changes in appetite, discuss testing with your GP. They can check vitamin and mineral levels via blood tests and recommend supplementation only if needed. Supplementing unnecessarily can lead to imbalances.
Is it safe to take iron supplements with Mounjaro?
Iron supplementation can be safe with Mounjaro, but timing matters. Take iron on an empty stomach (30 minutes before food) for best absorption, and separate it from other medications by at least 2 hours if possible. Because Mounjaro affects stomach acid and nutrient absorption, your GP may want to check your iron levels with a blood test before recommending supplementation.
Can I take omega-3 fish oil with Mounjaro?
Yes, omega-3 fish oil supplements are generally safe with Mounjaro. Fish oil may even support cardiovascular health and help manage triglycerides if needed. However, inform your GP if you're taking fish oil, especially if you're also taking blood-thinning medications. Stick to standard doses and choose high-quality supplements from reputable brands.
What should I do if I'm experiencing hair loss on Mounjaro — should I take biotin?
Hair loss (alopecia) is a reported side effect of Mounjaro, usually temporary and related to gradual weight management. Biotin supplementation may help support hair health, though evidence is mixed. More importantly, ensure you're getting enough protein, iron, and B vitamins — deficiencies worsen hair loss. Discuss hair loss with your GP; they may recommend blood tests to check nutrient levels before suggesting biotin or other supplements.
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