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 for Mounjaro: NHS UK Guidance
Mounjaro (tirzepatide) can affect nutrient absorption and appetite, making vitamin and mineral support important during treatment. Whilst Mounjaro is a prescription-only weight management injection licensed in the UK, understanding nutritional needs alongside your NHS or private treatment plan is essential. This guide covers the vitamins most relevant to Mounjaro users, NHS recommendations, and when to discuss supplementation with your GP or prescriber.
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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 Minerals to Consider During Mounjaro Treatment
Mounjaro works by reducing appetite and slowing gastric emptying, which means you may eat less food overall. This can lead to reduced intake of key nutrients. Vitamin B12 is particularly important—Mounjaro users sometimes experience reduced absorption, and B12 supports energy and nerve function. Iron may also decline with reduced food intake, especially for women of childbearing age. Calcium and vitamin D support bone health, which becomes relevant if weight loss is rapid. Folate (vitamin B9) is crucial, particularly for women of reproductive age, as deficiency poses risks during pregnancy.
- B12 supplements or B-complex vitamins may help maintain energy levels
- Iron levels should be monitored if you experience fatigue
- Calcium and vitamin D support bone density during weight loss
- Multivitamins may be beneficial but discuss with your GP first
Your GP or prescriber can arrange blood tests to check your vitamin and mineral levels, especially if you experience fatigue, weakness, or other symptoms.
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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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NHS Approach to Nutrition During Weight Loss Treatment
The NHS recommends a balanced, nutrient-dense diet during weight loss rather than relying on supplements alone. When tier 3 specialist weight management services prescribe Mounjaro through the NHS, they typically provide dietary guidance covering protein intake, micronutrient-rich foods, and hydration. gradual weight management—even with medication—increases nutritional risk.
Before starting any supplements, always inform your GP or prescriber. Some vitamins interact with medications or may not be necessary if your diet is well-planned. NHS dietitians can assess your individual needs and recommend appropriate supplements only when genuinely required. Use our free weight loss calculator to understand your treatment journey and discuss nutritional planning with your healthcare team.
The NHS recommends a balanced, nutrient-dense diet during weight loss rather than relying on supplements alone. When tier 3 specialist weight management services prescribe Mounjaro through the NHS, they typically provide dietary guidance covering protein intake, micronutrient-rich foods, and hydration. gradual weight management—even with medication—increases nutritional risk.
Before starting any supplements, always inform your GP or prescriber. Some vitamins interact with medications or may not be necessary if your diet is well-planned. NHS dietitians can assess your individual needs and recommend appropriate supplements only when genuinely required. Track your progress and discuss nutritional planning with your healthcare team using evidence-based guidance.
- 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 vitamin supplements while taking Mounjaro?
Not necessarily. If you maintain a balanced, nutrient-rich diet despite reduced appetite, you may not need supplements. However, blood tests through your GP may reveal deficiencies in B12, iron, or other nutrients. Only take supplements recommended by your prescriber or GP after assessment.
Is B12 supplementation common for Mounjaro users in the UK?
Some Mounjaro users experience reduced B12 absorption, though it is not universal. Your GP can test B12 levels if you experience fatigue or other symptoms. B12 supplements or injections may be recommended if deficiency is identified.
Can I take a standard multivitamin with Mounjaro?
A standard multivitamin is generally safe, but discuss it with your GP first. Some formulations may interfere with medication absorption or contain unnecessary nutrients. Your prescriber can recommend a vitamin product appropriate for your specific needs.
What does the NHS say about nutrition during weight loss treatment?
The NHS emphasises a balanced, whole-food diet rich in protein, vegetables, and micronutrient-dense foods over supplementation alone. Tier 3 services provide dietary guidance. Supplements fill gaps only when blood tests or symptoms indicate deficiency.
How do I know if I have a vitamin deficiency while on Mounjaro?
Signs include fatigue, weakness, hair loss, or brain fog. Request blood tests from your GP to check B12, iron, folate, and vitamin D levels. Do not self-diagnose—let your healthcare provider assess and recommend supplements based on results.
Ready to take control of your weight loss journey?
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