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 With Mounjaro?
When taking Mounjaro (tirzepatide) for weight management in the UK, vitamin and mineral supplementation may become important because the medication can affect how your body absorbs nutrients from food. Mounjaro slows gastric emptying — how quickly food moves through your stomach — which can impact nutrient absorption. Some people also eat smaller portions on Mounjaro, which may reduce overall nutrient intake. This guide explains which vitamins you might need, when to discuss supplementation with your GP, and how to protect your health during weight loss treatment.
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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 to Consider With Mounjaro
While taking Mounjaro, several vitamins and minerals warrant attention. B vitamins (B12, B6, folate) are commonly considered because reduced food intake may lower intake, and some people report fatigue on the medication. Iron becomes important if you're eating less red meat or plant-based iron sources. Calcium and vitamin D support bone health, especially important during weight loss when bone density can decline. Vitamin B12 specifically is sometimes recommended because Mounjaro may slightly reduce intrinsic factor needed for B12 absorption from food.
However, you should not start any supplementation without discussing it with your GP or prescribing clinician first. Taking certain vitamins alongside Mounjaro can affect medication absorption — your prescriber needs to review your individual diet, current medications, and health status before recommending supplements. Some people on Mounjaro have adequate nutrient intake from food and don't need supplements at all.
- Discuss your diet with your GP before starting any supplements
- Blood tests can identify specific deficiencies requiring treatment
- Timing of supplements relative to your Mounjaro injection may matter
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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.
Getting Mounjaro and Managing Nutrition in the UK
When accessing Mounjaro through the NHS specialist weight management service, your care team will monitor your nutritional status as part of your ongoing assessment. They can arrange blood tests to check for deficiencies and recommend appropriate supplementation. If you access Mounjaro through private online prescribing, your prescriber should discuss nutrition during your consultation, and you can ask about vitamin supplementation at that time.
The key is eating a balanced, nutrient-dense diet with lean proteins, vegetables, whole grains, and healthy fats — this minimises supplement need. Use our free GLP-1 weight loss calculator to understand your expected weight loss and plan nutrition accordingly. Your GP can also refer you to an NHS dietitian if you need specialist dietary advice while taking Mounjaro.
- 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 vitamins at the same time as my Mounjaro injection?
Generally yes, but timing matters. Some vitamins should be taken separately from medications that affect absorption. Discuss the specific supplements you're taking with your prescriber — they can advise on timing to avoid interactions with how Mounjaro affects your digestive system.
Does Mounjaro cause vitamin deficiencies?
Mounjaro doesn't directly cause deficiencies, but it can contribute to them indirectly by slowing digestion and reducing food intake. If you eat smaller portions or struggle with nausea, you may consume fewer nutrients. Blood tests can identify any deficiencies requiring treatment.
Should everyone taking Mounjaro take B12 supplements?
No. Whether you need B12 supplements depends on your current diet, baseline B12 levels, and how Mounjaro affects your eating. A blood test can show your B12 status. Your GP can recommend supplementation if needed, rather than taking it routinely.
Can I take vitamin supplements with oral medications on Mounjaro?
Mounjaro may affect how your body absorbs oral medications and supplements. If you take oral contraceptives or other medications, inform your prescriber about any supplements you're considering — they may need adjusting or timing differently.
What should I eat on Mounjaro to get enough nutrients naturally?
Prioritise protein (fish, chicken, eggs, beans), vegetables for fibre and micronutrients, whole grains, and healthy fats. Even smaller portions can be nutrient-dense if you focus on quality foods. Your GP can refer you to a dietitian for personalised advice on nutrition while on tirzepatide.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.