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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What Vitamins Should You Take When On Mounjaro?
When taking Mounjaro (tirzepatide) for weight management, your body's nutritional needs may change. As an appetite-reducing medication, Mounjaro can affect how much food you eat and how your body absorbs certain nutrients. This means some people may benefit from vitamin supplementation during treatment. However, any supplement plan should be discussed with your GP first, as individual needs vary based on your health history, diet, and the specific Mounjaro dose you're taking. This guide covers the vitamins commonly discussed during Mounjaro treatment and how to approach nutritional support safely.
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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.
Vitamins and Nutrients Commonly Discussed With Mounjaro
When taking Mounjaro, reduced food intake can sometimes mean lower intake of essential vitamins and minerals. Key nutrients that healthcare professionals often monitor or recommend supplementing include:
- Vitamin B12 — Important for energy and nerve function. Mounjaro may reduce absorption of some B vitamins, particularly if you have reduced stomach acid.
- Iron — Especially important for women of childbearing age. Reduced food intake may lower iron consumption.
- Calcium and Vitamin D — Essential for bone health. Lower food intake can reduce calcium intake, particularly if dairy consumption decreases.
- Protein — While not a vitamin, adequate protein is crucial during weight loss to preserve muscle mass. Ensure sufficient intake through food or supplements as recommended by your GP.
- Folate and B vitamins — Support metabolism and energy. These are particularly important if you're of childbearing age.
Your GP or a registered dietitian can assess your individual dietary intake and recommend appropriate supplements based on blood tests if needed. Regular monitoring helps ensure you're meeting your nutritional needs whilst taking Mounjaro.
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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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How to Approach Supplements Safely While Taking Mounjaro
Before starting any vitamin or supplement whilst on Mounjaro, always inform your prescriber or GP. Some supplements may interact with medications or affect how well Mounjaro works. Your healthcare team can advise on safe, evidence-based options.
Consider asking your GP about having a blood test to check your nutrient levels — particularly vitamin B12, iron, and vitamin D — before starting Mounjaro and periodically during treatment. This helps identify genuine deficiencies rather than guessing. A registered dietitian can also provide personalised nutrition advice tailored to your reduced appetite and food preferences. Keep a food diary temporarily to show your healthcare provider, as this helps them assess whether you actually need supplements or if dietary adjustments might be sufficient first.
- 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 multivitamins whilst on Mounjaro?
Yes, most people can take multivitamins alongside Mounjaro, but discuss this with your GP first. Some multivitamins contain ingredients that might interact with other medications you're taking. A standard, UK-licensed multivitamin is usually safe, but your prescriber needs to know about all supplements you're considering.
Why might I need B12 supplementation on Mounjaro?
Mounjaro can reduce the amount of food you eat, which may lower your overall B12 intake from dietary sources like meat and dairy. Additionally, reduced stomach acid (which sometimes occurs with GLP-1 medications) can affect B12 absorption. Your GP can test your B12 levels and recommend supplementation if needed.
Should I take supplements before or after my Mounjaro injection?
Timing of supplements relative to your Mounjaro injection is generally not critical. However, some supplements are better absorbed with food, whilst others are better on an empty stomach. Your pharmacist or GP can advise on the best timing for your specific supplements.
What if I'm feeling fatigued or weak on Mounjaro — could it be vitamin deficiency?
Fatigue can have multiple causes, including gradual weight management, reduced calorie intake, or underlying health conditions. Discuss your symptoms with your GP, who can arrange blood tests to check for deficiencies in iron, B12, vitamin D, and other nutrients. Never self-diagnose or self-supplement without professional guidance.
Do I need supplements if I'm eating a balanced diet on Mounjaro?
Not necessarily. If you're eating a varied, balanced diet including protein, fruit, vegetables, and fortified foods, you may not need supplements. However, reduced appetite can make this challenging. Your GP or dietitian can assess your actual intake and recommend supplements only if there's a genuine nutritional gap.
Ready to take control of your weight loss journey?
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