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 I Take With Mounjaro?
If you're taking Mounjaro (tirzepatide), you may wonder whether you need additional vitamins or supplements. The answer depends on how the medication affects your digestion and your individual nutritional intake. Mounjaro slows stomach emptying and can reduce appetite significantly, which may mean you're eating less overall. This raises the risk of certain nutrient deficiencies. Your GP or prescriber should monitor your nutritional health, but understanding which vitamins matter most can help you have an informed conversation with your healthcare team about supplementation.
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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 Affects Vitamin and Mineral Absorption
Mounjaro works by slowing how quickly food moves through your stomach (gastric emptying) and reducing your appetite. While this helps with weight loss, it can affect how your body absorbs certain nutrients, especially in the first weeks of treatment. Additionally, because appetite is reduced, many people naturally eat smaller portions—which means fewer calories and potentially fewer vitamins and minerals overall.
Key concerns include:
- B vitamins (B12, B6, folate): Required for energy and nervous system function. Reduced food intake may lower intake of B12-rich foods like meat and dairy.
- Iron: Essential for oxygen transport. Women of reproductive age are particularly at risk if eating less red meat or fortified foods.
- Calcium and Vitamin D: Critical for bone health, especially if you're losing weight quickly.
- Protein: Not technically a vitamin, but essential. Mounjaro users should prioritise protein intake to preserve muscle during weight loss.
Your prescriber may recommend blood tests to check for deficiencies before and during treatment. This is especially important if you experience persistent nausea, vomiting, or severe appetite suppression.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Which Supplements Are Safe to Take With Mounjaro?
Most standard multivitamins, B vitamin supplements, and mineral supplements are safe to take alongside Mounjaro, but timing and form matter. Because Mounjaro slows stomach emptying, oral medications and supplements may not be absorbed as efficiently if taken simultaneously with food or each other.
General guidance:
- Take supplements at least 30 minutes to 1 hour before or after meals to maximise absorption.
- Liquid or chewable supplements may be absorbed better than tablets if you have persistent nausea.
- Vitamin B12 may be better absorbed via injection (given by your GP) rather than oral supplements, especially if you're concerned about deficiency.
- Always inform your prescriber of all supplements you're taking—some may interact with Mounjaro or affect how it works.
Never start high-dose supplementation without checking with your GP first, as excessive intake of fat-soluble vitamins (A, D, E, K) can accumulate in your body.
- 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 while on Mounjaro?
Yes, most standard multivitamins are safe to take with Mounjaro. However, take it separately from meals and Mounjaro injections—ideally 30 minutes to 1 hour before or after eating. This improves absorption given that Mounjaro slows stomach emptying. Always mention your multivitamin to your prescriber to rule out any interactions.
Is B12 supplementation necessary when taking Mounjaro?
Not necessarily for everyone, but it's worth discussing with your GP. If you're experiencing reduced appetite and eating fewer B12-rich foods (meat, dairy, eggs), your levels may drop over time. Your prescriber may recommend B12 blood tests. Injected B12 given by your GP is often more effective than oral supplements for Mounjaro users.
Should I take supplements with food or on an empty stomach with Mounjaro?
Take supplements on an empty stomach or at least 30 minutes to 1 hour away from meals. Because Mounjaro slows how quickly food leaves your stomach, taking supplements with food can reduce absorption. This timing also helps prevent interactions between the medication and other substances.
Can Mounjaro cause vitamin deficiencies?
Mounjaro itself doesn't directly cause deficiencies, but its effects do increase the risk. By reducing appetite and slowing digestion, you may consume fewer calories and nutrients overall. Regular blood tests recommended by your prescriber can detect early deficiencies, allowing supplementation before symptoms develop.
Will my GP monitor my vitamin levels while taking Mounjaro?
Your prescriber should monitor your nutritional health, especially if you're losing weight quickly or experiencing persistent nausea. Ask about baseline blood tests and whether follow-up testing is planned. If you have concerns about specific nutrients or side effects, discuss supplementation with your GP—they can recommend appropriate doses tailored to you.
Ready to take control of your weight loss journey?
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