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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Best Vitamins To Take When On Mounjaro
Mounjaro (tirzepatide) is a prescription-only weight management injection that works by activating GIP and GLP-1 hormone pathways. Because the medication reduces appetite and slows gastric emptying, some people may eat less food overall, which can affect nutrient intake. While Mounjaro itself doesn't directly cause vitamin deficiencies, certain micronutrients are worth monitoring during treatment. This guide explores which vitamins and supplements may be beneficial whilst on this medication, and why your GP should guide any supplementation choices.
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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.
Nutrients of Concern When Taking Mounjaro
When taking tirzepatide (Mounjaro), reduced food intake may lead to lower consumption of certain key nutrients. The main vitamins and minerals worth monitoring include B12, B6, folate, iron, and calcium. Some people report experiencing hair loss (alopecia) whilst on the medication, which may indicate deficiencies in biotin, zinc, or iron — though this can also be a direct side effect unrelated to nutrition.
- Vitamin B12: Essential for energy and nervous system health. Found in meat, fish, dairy, and fortified cereals.
- Vitamin D: Important for bone health and immune function, especially relevant given reduced sun exposure in the UK during winter months.
- Iron: Supports oxygen transport. Slowed digestion may reduce iron absorption from food.
- Calcium: Critical for bone density, particularly important if experiencing reduced dairy intake.
- Folate and B vitamins: Support energy metabolism and overall health during weight loss.
Before starting any new supplement whilst on Mounjaro, discuss with your GP. Some supplements may interact with the medication or affect how well it works.
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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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Timing and Practical Supplementation Advice
If your GP recommends vitamins or supplements whilst on Mounjaro UK prescription treatment, timing matters. Because the medication slows stomach emptying, take supplements with food to improve absorption. Avoid taking them at the exact same time as Mounjaro injections — space them out by at least a few hours. Liquid supplements or gummies may be easier to tolerate than large tablets if you're experiencing nausea as a side effect.
A simple blood test through your GP can check your nutrient levels after you've been on Mounjaro for a few months. This removes guesswork and ensures any supplementation is genuinely needed. Keep a food diary during your first weeks of treatment to spot any obvious nutrient gaps. Our free progress tracker can help you log your weight loss journey and any side effects you notice, which you can then discuss with your prescriber at follow-up appointments.
- 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, a standard multivitamin is generally safe alongside Mounjaro. However, discuss with your GP first, as some supplements may affect medication absorption. Your prescriber may recommend specific vitamins based on your diet and blood work rather than a one-size-fits-all multivitamin.
Why might I need more B12 on Mounjaro?
B12 is found mainly in animal products, and reduced food intake on Mounjaro may lower overall B12 consumption. Additionally, slowed gastric emptying may slightly reduce B12 absorption. Your GP can check B12 levels via a simple blood test and recommend supplementation if needed.
Does Mounjaro cause vitamin deficiencies directly?
Mounjaro itself doesn't directly deplete vitamins. However, because it reduces appetite, some people eat less food overall, which can reduce nutrient intake. Hair loss reported by some users may indicate iron or zinc deficiency, though this can also be a direct medication side effect.
Should I take supplements at the same time as my Mounjaro injection?
No — space supplements out from your Mounjaro injection by at least a few hours. Because the medication slows stomach emptying, take vitamins with food to improve absorption. Avoid taking multiple medications or supplements simultaneously unless your GP advises otherwise.
How do I know which vitamins I actually need?
Your GP can order blood tests to check nutrient levels (B12, vitamin D, iron, folate) after you've been on Mounjaro for 2–3 months. This is far more reliable than guessing. Targeted supplementation based on actual test results is more effective than taking everything "just in case."
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