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 When On Mounjaro — Nutrient Support Guide
When taking Mounjaro (tirzepatide) for weight management, your body's nutrient needs change — especially as your appetite naturally decreases and meal portions reduce. Certain vitamins and minerals become harder to get through food alone. This guide explains which nutrients matter most when on Mounjaro, what deficiencies to watch for, and how to supplement safely. Always discuss any new supplements with your GP before starting them, as some may interact with other medications you're taking.
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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 Nutrients to Monitor on Mounjaro
As Mounjaro reduces appetite and slows gastric emptying, your body absorbs fewer nutrients from smaller food portions. The most important vitamins and minerals to prioritise are:
- Vitamin B12 — Essential for energy and nerve function. Mounjaro slows stomach acid, which can reduce B12 absorption. Consider B12 supplements or injections.
- Vitamin D — Many UK adults are deficient, especially in winter. Mounjaro users eating less may further reduce intake. A supplement of 1,000–2,000 IU daily is often recommended.
- Iron — Reduced food intake can lower iron levels, particularly important for women of reproductive age. Get levels checked before supplementing.
- Calcium — Slower gastric transit may reduce calcium absorption. Aim for 1,000–1,200 mg daily through food or supplements.
- Electrolytes (sodium, potassium, magnesium) — Nausea, vomiting, and diarrhoea — common Mounjaro side effects — can deplete electrolytes. Monitor symptoms and consider electrolyte replacement drinks.
Your GP or a registered dietitian can test your nutrient levels and recommend personalised supplementation based on your individual needs and Mounjaro dose titration stage.
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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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Safety, Timing, and Supplement Interactions
Never start new supplements without consulting your GP — some may interact with Mounjaro or other medications, or interfere with absorption. Timing matters: take oral supplements at least 1–2 hours before or after your weekly Mounjaro injection to avoid interference. Liquid or sublingual supplements (like B12 spray) may be absorbed better than tablets when on Mounjaro, since the medication slows gastric emptying.
If you experience persistent nausea, vomiting, or diarrhoea on Mounjaro, electrolyte depletion becomes more likely — ask your GP or a dietitian about monitoring and replacement. Many people find a high-quality multivitamin designed for post-bariatric patients helpful, as these are formulated for reduced food intake. Check with your healthcare provider about the best option for your specific situation and current Mounjaro dose.
- 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?
Many people benefit from supplementation while on Mounjaro, as reduced appetite and smaller meal portions lower nutrient intake. B12, vitamin D, iron, calcium, and electrolytes are the most common deficiencies. Your GP can test your levels and advise whether supplements are needed for your individual situation.
Can vitamins interact with Mounjaro?
Some supplements may interfere with Mounjaro's absorption or interact with other medications. Always discuss new supplements with your GP before starting. Take oral supplements at least 1–2 hours away from your weekly Mounjaro injection to minimise interference.
What if I'm experiencing nausea and diarrhoea on Mounjaro?
Nausea, vomiting, and diarrhoea are common Mounjaro side effects that deplete electrolytes and reduce nutrient absorption. Speak to your GP about monitoring electrolyte levels and whether replacement drinks or supplements are needed. These side effects usually improve as your body adjusts to the medication.
Is a multivitamin enough, or do I need individual supplements?
A standard multivitamin may not provide enough of the nutrients most depleted by Mounjaro. A high-strength multivitamin designed for weight loss or post-bariatric surgery, combined with targeted B12 and vitamin D, is often more effective. Your GP or a registered dietitian can recommend the best approach for you.
How can I track if my nutrient levels are healthy on Mounjaro?
Ask your GP for baseline blood tests (B12, vitamin D, iron, calcium, magnesium) before starting Mounjaro, then follow-up tests at 3–6 months. Our free progress tracker can help you monitor energy, mood, and digestion symptoms — signs that may suggest nutrient deficiency. Regular GP check-ins ensure supplementation matches your needs as your Mounjaro dose titration progresses.
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.