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 Supplements to Take With Mounjaro
If you're taking Mounjaro (tirzepatide) as part of your weight management journey, you may wonder which supplements are safe to use alongside your treatment. Because Mounjaro slows gastric emptying and can affect how your body absorbs certain nutrients, supplementation may become important. This guide explains which supplements are commonly recommended alongside Mounjaro, how to take them safely, and when to discuss supplementation with your GP or prescriber. Always check with your healthcare provider before starting any new supplement whilst on Mounjaro.
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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.
Key Supplements to Consider With Mounjaro
Vitamin B12 deficiency is common when taking Mounjaro because the medication slows stomach acid production and nutrient absorption. Many people on Mounjaro benefit from B12 supplementation, either as oral tablets, sublingual lozenges, or injections prescribed by your GP.
Iron supplements may be needed if your diet lacks red meat or plant-based iron sources. Take iron supplements 2–4 hours away from Mounjaro injections to avoid absorption interference.
Calcium and vitamin D support bone health, especially important during weight loss when bone density can shift. These are fat-soluble vitamins and are generally safe alongside Mounjaro.
- Take calcium supplements 2+ hours apart from other medications
- Vitamin D (cholecalciferol) supports calcium absorption
- Many UK adults are vitamin D deficient, particularly in winter months
- Request a vitamin D blood test from your GP if unsure of your levels
Before starting any supplement, discuss it with your prescriber. Some supplements may interact with other medications you take, or may not be necessary if your diet is already adequate in those nutrients.
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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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Supplements to Avoid or Be Cautious With
Fat-soluble vitamins (A, D, E, K) are absorbed differently when taking Mounjaro due to slowed gastric transit. This doesn't mean you should avoid them, but absorption may be less efficient—your GP or a registered dietitian can advise whether supplementation is needed.
Oral contraceptive pills and other oral medications have reduced absorption with Mounjaro. If you take any oral medication, space it at least 30 minutes to 2 hours away from food and at a separate time from your injection. Discuss any concerns with your GP.
- Herbal supplements may interact with Mounjaro—always declare them to your prescriber
- High-dose supplements can occasionally cause stomach upset when combined with Mounjaro
- Fibre supplements may worsen constipation or diarrhoea if not managed carefully
- 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.
Should I take supplements with Mounjaro?
Many people benefit from B12, iron, calcium, and vitamin D supplementation whilst on Mounjaro because the medication affects nutrient absorption. However, supplementation is individual—request blood tests from your GP to identify any deficiencies before starting supplements. Not everyone will need supplements if their diet is adequate.
Can I take vitamins with Mounjaro on the same day?
Yes, most water-soluble vitamins (B vitamins, vitamin C) can be taken on the same day as your Mounjaro injection. However, space oral medications at least 30 minutes to 2 hours apart. Fat-soluble vitamins (A, D, E, K) are absorbed less efficiently with Mounjaro, so discuss with your GP whether supplementation is necessary.
Does Mounjaro affect B12 absorption?
Mounjaro slows stomach acid production, which is needed to absorb B12 from food. Many people on Mounjaro develop or are at risk of B12 deficiency. Your GP can order blood tests to check your B12 levels and may recommend oral supplements or injections if levels are low.
Is it safe to take multivitamins with Mounjaro?
Multivitamins are generally safe with Mounjaro, but they're only necessary if your diet lacks specific nutrients. A standard multivitamin won't harm you, but individual supplementation based on blood test results is often more effective. Discuss with your GP or a registered dietitian before taking a daily multivitamin.
What should I eat to avoid needing supplements on Mounjaro?
Eat nutrient-dense foods: red meat or poultry for iron and B12, dairy or fortified plant milks for calcium, fatty fish or egg yolks for vitamin D, and varied vegetables for micronutrients. Because Mounjaro reduces appetite, making each calorie count nutritionally is important. A registered dietitian can help you plan a balanced diet that meets your needs.
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