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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Which Vitamins Should You Take With Mounjaro?
If you're taking Mounjaro (tirzepatide) for weight management, you may want to know whether vitamin or mineral supplements are needed. Mounjaro doesn't directly cause nutritional deficiencies, but the reduced food intake that often accompanies weight loss can affect nutrient absorption. This guide explains what vitamins matter when using Mounjaro, which nutrients to monitor, and when to speak with your GP or a registered dietitian about supplementation to support your health during weight loss.
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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.
Nutrients To Monitor When Taking Mounjaro
When using Mounjaro, your food intake typically decreases as you feel fuller on smaller portions. This means you may consume fewer calories and, potentially, fewer nutrients overall. Key nutrients to monitor include:
- Vitamin B12 — important for energy and nerve function; found in meat, fish, eggs, and dairy
- Iron — especially important for women; found in red meat, beans, and fortified cereals
- Calcium and vitamin D — essential for bone health; may be reduced if you're consuming less dairy
- Protein — critical during weight loss to preserve muscle mass; aim for adequate protein at each meal
- Fibre — Mounjaro can cause constipation or diarrhoea; adequate fibre and hydration help manage this
A balanced, nutrient-dense diet — focusing on whole foods rather than processed options — is the best approach. Your GP or a registered dietitian can assess whether you personally need supplementation based on your diet and blood test results.
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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.
When To Consider Vitamin Supplements
You may benefit from vitamin supplementation if:
- Blood tests show deficiencies in B12, iron, calcium, or vitamin D
- You follow a restricted diet (vegetarian, vegan, or allergy-related)
- You experience persistent side effects like diarrhoea that affect nutrient absorption
- You have a known malabsorption condition
Always discuss any supplements or vitamins with your GP or the prescriber managing your Mounjaro treatment before starting them. Some supplements may interact with medications or affect how Mounjaro works. A registered dietitian can provide personalised guidance on what's right for your individual situation and dietary choices during your weight loss 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, nutrient-rich diet with adequate protein, whole grains, fruits, and vegetables, you may not need supplements. However, if your food intake is significantly reduced or you have dietary restrictions, your GP may recommend specific supplements based on blood tests or your individual health.
Will Mounjaro cause vitamin deficiencies?
Mounjaro itself doesn't directly cause deficiencies, but reduced food intake during weight loss can. The most common concerns are B12, iron, calcium, and vitamin D. Regular GP check-ups and potentially blood tests can monitor your nutrient levels, especially if you're losing weight over several months.
Is vitamin B12 supplementation necessary with Mounjaro?
Only if you're deficient. B12 is found mainly in animal products (meat, fish, dairy, eggs). If you eat these regularly, supplementation isn't usually needed. Vegetarians and vegans should discuss B12 screening with their GP, regardless of Mounjaro use.
Can I take supplements while taking Mounjaro?
Most vitamins and minerals are safe alongside Mounjaro, but some supplements may slow gastric emptying or interact with other medications. Always inform your prescriber or GP about any supplements you're taking before starting them.
What's the best way to get vitamins while on Mounjaro?
Prioritise nutrient-dense whole foods first — lean proteins, colourful vegetables, fruits, whole grains, and dairy or fortified alternatives. Use our GLP-1 weight loss calculator to understand your calorie needs, then work with a dietitian to build a balanced meal plan that meets nutritional targets while supporting your weight loss goals.
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.