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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Vitamins and Nutrients When Taking Mounjaro
When using Mounjaro (tirzepatide) for weight management, your body's nutritional needs may change significantly. As your appetite decreases and food intake reduces, you may absorb fewer vitamins and minerals naturally. This guide explains which vitamins matter most, how to identify deficiencies, and when to speak to your GP. Always discuss any supplement plan with your healthcare provider before starting, as some interactions are possible with Mounjaro and other medications.
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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 Vitamins and Minerals on Mounjaro
As you lose weight on Mounjaro, your reduced food intake can lead to lower levels of essential nutrients. The vitamins and minerals most commonly affected include B12, iron, calcium, vitamin D, and folate. Your GP may recommend a blood test to check your baseline nutrient levels before starting treatment, and periodic checks during your weight loss journey. B12 injections or supplements are particularly common for Mounjaro users, as the medication can affect how your stomach absorbs this vitamin. Many people benefit from a quality multivitamin designed for weight loss or bariatric patients, though individual needs vary. Never start supplements without discussing with your prescriber or GP, as some vitamins can interact with other medications you may be taking, and some may affect how Mounjaro works. A blood test is the only reliable way to identify genuine deficiency rather than guessing.
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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.
Accessing Nutritional Support on NHS and Privately
If you're accessing Mounjaro through the NHS via a specialist weight management service, your tier 3 or tier 4 team should monitor your nutrition and recommend supplements where needed. If you're using Mounjaro privately through an online consultation, your prescriber will give guidance, though you may need to arrange blood tests separately with your GP. Private blood tests are available quickly if needed. When selecting supplements, look for products specifically formulated for people on weight loss medication — these typically contain the key nutrients at appropriate doses. Always keep your GP informed about any supplements you're taking, as they're responsible for your overall health monitoring. Our GLP-1 weight loss calculator can help you understand your expected weight loss, but nutritional planning should always involve your healthcare team. Vitamin supplementation is a practical, low-cost step that can prevent deficiency-related fatigue or health problems during your weight loss journey.
- 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 definitely need vitamin supplements when taking Mounjaro?
Not necessarily — it depends on your individual circumstances, baseline nutrition, and how much weight you lose. Some people eating a balanced diet don't become deficient. A blood test from your GP can confirm whether you need supplements rather than taking them preventatively. Always discuss with your prescriber or GP before starting any supplement routine.
Which vitamin is most important when on Mounjaro?
B12 is often highlighted because Mounjaro can reduce stomach acid, affecting B12 absorption. Iron and vitamin D are also commonly monitored. However, individual needs vary — a blood test is the most reliable way to identify your specific deficiencies rather than assuming all Mounjaro users need the same supplements.
Can I take multivitamins with Mounjaro?
Yes, multivitamins are generally safe with Mounjaro, but always check with your GP or prescriber first. Some vitamins can interact with other medications you may be taking. Avoid taking supplements at the same time as oral medications — space them out by a few hours since Mounjaro slows stomach emptying.
How do I know if I'm deficient in vitamins on Mounjaro?
Signs include fatigue, weakness, hair loss, pale or yellow skin, and tingling in hands or feet. However, these can have other causes. The only reliable way to identify deficiency is a blood test from your GP — don't guess based on symptoms alone. Request monitoring from your healthcare provider as part of your weight loss journey.
Can I get vitamin blood tests through the NHS?
Yes — your GP can arrange basic nutrient testing on the NHS. If you're using Mounjaro privately, ask your GP for blood tests to check B12, iron, folate, and vitamin D levels. Some private clinics offer these tests quickly if NHS waiting times are long in your area. Regular monitoring helps prevent deficiency problems.
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.