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
Free tracker included with every download this week
Taking Vitamins While On Mounjaro
When taking Mounjaro (tirzepatide) for weight management, your body's ability to absorb nutrients from food may change. Since Mounjaro slows how quickly food passes through your stomach, some vitamins and minerals may not be absorbed as efficiently as usual. This guide explains the nutrient considerations you should discuss with your GP or prescriber, and why supplementation might be recommended during your weight loss journey.
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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.
Why Nutrient Absorption Matters on Mounjaro
Mounjaro works by slowing gastric emptying — the rate at which food moves from your stomach into your small intestine. While this helps create feeling fuller after smaller meals, it can also affect how your digestive system absorbs certain vitamins and minerals. Additionally, gradual weight management itself can deplete nutrient stores, particularly B vitamins, iron, calcium, and vitamin D.
- B vitamins: Essential for energy and metabolism — deficiency can cause fatigue and weakness
- Vitamin D: Critical for bone health and immunity — often deficient in UK adults
- Iron: Risk of anaemia if stores become depleted during weight loss
- Calcium: Important for bone density, especially for women
- Magnesium: Supports muscle and nerve function
Your prescriber should assess your baseline nutritional status and may recommend blood tests before starting Mounjaro and periodically during treatment.
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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.
Which Vitamins Should You Consider Taking?
There is no single universal vitamin protocol for Mounjaro users — recommendations depend on your individual baseline health, diet, and blood test results. However, many people benefit from a general multivitamin or B-complex supplement as a precaution. Your GP or a registered dietitian can order baseline blood tests to check your levels of key nutrients before you start Mounjaro, then recommend specific supplementation based on your results.
Some prescribers recommend a daily multivitamin alongside Mounjaro as routine practice. Take any vitamin supplements with food and allow at least 2 hours between taking Mounjaro and oral medications or supplements to avoid absorption issues. Always inform your prescriber of any supplements you are taking.
- 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.
Can I take vitamins and Mounjaro at the same time?
You can take vitamins while on Mounjaro, but timing matters. Allow at least 2 hours between Mounjaro injection and oral vitamin tablets or supplements to maximise absorption. Take vitamins with food. Always tell your prescriber what supplements you're taking, as some may interact with other medications.
Will Mounjaro cause vitamin deficiencies?
Mounjaro slows stomach emptying, which may reduce nutrient absorption slightly. Combined with gradual weight management, this can deplete certain vitamins — particularly B vitamins, vitamin D, iron, and calcium. Blood tests before and during treatment help identify deficiencies early so your prescriber can recommend appropriate supplementation.
Should I take a multivitamin on Mounjaro?
Many people benefit from a daily multivitamin while on Mounjaro, but it's not mandatory for everyone. Your prescriber or GP will assess your individual risk based on your baseline blood tests, diet, and medical history. A registered dietitian can provide personalised supplementation advice alongside your weight loss plan.
What about oral contraceptives and supplements with Mounjaro?
Mounjaro may reduce absorption of oral medications, including contraceptive pills. If you take oral contraceptives, add a barrier contraceptive method for 4 weeks after starting Mounjaro and 4 weeks after each dose increase. Discuss all medications and supplements with your prescriber.
How do I track nutritional status while using Mounjaro?
Your prescriber should offer baseline blood tests before starting Mounjaro, checking B12, folate, iron, calcium, vitamin D, and other key nutrients. Regular follow-up tests — typically every 3–6 months — help monitor levels and adjust supplementation. You can also track your overall progress using our free progress tracker to monitor weight loss alongside energy and wellbeing.
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.