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?
If you're taking Mounjaro (tirzepatide) for weight management in the UK, understanding nutritional support is important. Because Mounjaro slows gastric emptying and can reduce appetite, some people may absorb fewer nutrients or eat smaller portions. While there's no single NHS-approved vitamin protocol for Mounjaro users, certain supplements may help prevent deficiencies during treatment. This guide covers what vitamins are typically recommended, when to take them, and how 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 Supplements Commonly Recommended With Mounjaro
There is no mandatory vitamin regimen for Mounjaro users in the UK, but clinical practice often supports supplementation because reduced appetite and slower stomach emptying can affect nutrient absorption.
Commonly recommended vitamins include:
- Vitamin B12 — GLP-1 and dual agonists like tirzepatide may reduce B12 absorption; B12 deficiency can cause fatigue and neuropathy. A B12 spray, injection, or high-dose oral supplement may be advised.
- Iron — Reduced food intake may lower iron consumption, particularly important for women of reproductive age. A GP may recommend iron supplementation or monitoring.
- Calcium and vitamin D — Essential for bone health, especially during weight loss when bone density can decrease. Many GPs recommend a combined supplement.
- Multivitamin — A general multivitamin tailored to reduced calorie intake can act as a safety net, though it should be discussed with your prescriber first.
Always consult your GP or prescriber before starting any supplement, as some may interact with Mounjaro or other medications you're taking.
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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.
Taking Vitamins With Mounjaro — Timing and Absorption
Because Mounjaro slows how quickly food leaves your stomach, taking vitamins at the right time matters. Take most oral supplements on an empty stomach or with a light meal — not immediately after taking Mounjaro or if you're experiencing nausea or vomiting.
Avoid taking oral medications or supplements within 4 hours of a large meal when on Mounjaro, as gastric emptying delays may reduce absorption. Vitamin B12 and iron are best absorbed separately from calcium and some other minerals, so spacing them out during the day is ideal.
If you experience persistent nausea, reduced appetite, or gastrointestinal symptoms that worry you, mention this to your GP. They may recommend injected B12 or adjusted supplementation to ensure you're getting adequate nutrition while on tirzepatide treatment in the UK.
- 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 have to take vitamins while on Mounjaro in the UK?
No, there's no mandatory vitamin regimen for Mounjaro users. However, because the medication reduces appetite and slows stomach emptying, your GP may recommend supplementation to prevent deficiencies in B12, iron, calcium, or vitamin D. Always discuss with your prescriber first.
Can I take my usual multivitamin with Mounjaro?
Possibly, but check with your GP or prescriber first. Some multivitamins may contain ingredients that interact with Mounjaro or reduce absorption. Timing is important—take supplements with light meals or on an empty stomach, not during peak Mounjaro effects.
Is B12 supplementation needed with tirzepatide?
GLP-1 and dual agonist medications like tirzepatide may reduce B12 absorption, and reduced food intake can lower B12 intake overall. Many UK prescribers recommend B12 monitoring or supplementation (spray, injection, or high-dose oral) as a precaution, especially after 6–12 months.
Can I use our GLP-1 weight loss calculator to track nutritional changes?
The calculator helps project weight loss at different Mounjaro doses, but it doesn't track nutrition directly. However, alongside your progress tracker, monitoring your weight loss rate helps identify whether supplementation is needed—rapid loss without proper nutrition support can deplete muscle and bone density.
Should I space out vitamin supplements from my Mounjaro injection?
Yes. Take most oral supplements on an empty stomach or with light meals, not immediately after eating a large meal or around the time Mounjaro effects peak (usually the first few hours after injection or during the day). Space calcium, iron, and B12 separately if possible for better absorption.
Ready to take control of your weight loss journey?
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