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), your body's nutritional needs may change due to reduced food intake and altered stomach function. While there is no single "Mounjaro vitamin list" recommended by the NHS, certain nutrients become more important to monitor. This guide covers the key vitamins and minerals to discuss with your GP or prescriber, and how to maintain good nutritional health while using this prescription weight management injection alongside a reduced-calorie diet.
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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.
Key Nutrients to Monitor on Mounjaro
Mounjaro works by slowing gastric emptying and reducing appetite, which means you'll eat less food overall. This can lead to lower intake of certain essential nutrients. Key nutrients to discuss with your GP include:
- Vitamin B12 — important for energy and nerve function; stomach changes may reduce absorption
- Iron — especially important for women of childbearing age; reduced food intake can lower dietary iron
- Calcium and Vitamin D — critical for bone health, particularly if weight loss is rapid
- Protein — helps preserve muscle mass during weight loss; aim for adequate protein at each meal
- Folate (Vitamin B9) — reduced vegetable intake may lower folate levels
- Electrolytes — sodium, potassium, and magnesium may need monitoring, especially if experiencing diarrhoea or constipation
Your prescriber may recommend a standard multivitamin or specific supplementation based on your individual health profile. Always check with your GP before starting any new supplements, as some may interact with other medications.
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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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Nutritional Best Practice While on Mounjaro
Rather than relying solely on supplements, the NHS advises prioritising nutrient-dense foods within your reduced calorie intake. Include lean proteins, colourful vegetables, whole grains, and healthy fats to maximise nutritional value from smaller portion sizes. Staying hydrated is equally important — aim for 6–8 glasses of water daily, especially if experiencing nausea or digestive changes.
If you experience persistent nausea, vomiting, or constipation on Mounjaro, speak to your GP or pharmacist. These side effects can affect nutrient absorption and appetite. Your healthcare team may suggest dietary adjustments or recommend specific vitamins. Try our free weight loss calculator to monitor your progress and identify any patterns between diet and side effects.
Rather than relying solely on supplements, the NHS advises prioritising nutrient-dense foods within your reduced calorie intake. Include lean proteins, colourful vegetables, whole grains, and healthy fats to maximise nutritional value from smaller portion sizes. Staying hydrated is equally important — aim for 6–8 glasses of water daily, especially if experiencing nausea or digestive changes.
If you experience persistent nausea, vomiting, or constipation on Mounjaro, speak to your GP or pharmacist. These side effects can affect nutrient absorption and appetite. Your healthcare team may suggest dietary adjustments or recommend specific vitamins. Track your nutritional intake and side effects to share with your prescriber, and use our free BMI calculator to monitor your health progress throughout your weight management journey.
- 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.
Do I need to take vitamins while on Mounjaro?
Not necessarily. If you eat a balanced diet with plenty of protein, vegetables, and whole grains, you may not need supplements. However, reduced food intake can lower certain nutrients. Your GP or prescriber can assess your individual needs and recommend supplements if necessary. Always discuss this at your clinic review appointments.
Can Mounjaro affect vitamin absorption?
Yes. Mounjaro slows stomach emptying and reduces food intake, which can affect how your body absorbs nutrients from food. Additionally, reduced stomach acid (which some people experience) may lower B12 absorption. This is why monitoring and discussing supplementation with your healthcare team is important.
Is a multivitamin enough when taking Mounjaro?
A standard multivitamin may help cover basic nutritional gaps. However, your specific needs depend on your diet, other health conditions, and any side effects you experience. Your GP may recommend specific supplements like B12, iron, or calcium rather than a generic multivitamin. Always get personalised advice.
What if I'm struggling to eat enough protein on Mounjaro?
Reduced appetite is common on Mounjaro. If you cannot meet protein needs through food alone, your prescriber may recommend protein supplements (shakes or powders). Protein is crucial for preserving muscle mass during weight loss. Discuss your diet with your healthcare team at each review.
Should I take supplements at the same time as Mounjaro?
Mounjaro may affect the absorption of oral medications and supplements because it slows stomach emptying. Space out supplements by at least 30 minutes to 1 hour from your Mounjaro injection if possible. Speak to your pharmacist about optimal timing based on the specific supplements you're taking.
Ready to take control of your weight loss journey?
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