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
What Vitamins Should You Take With Mounjaro?
When taking Mounjaro (tirzepatide), vitamin and mineral absorption can be affected because the medication slows stomach emptying and reduces food intake. Your GP or prescriber may recommend specific supplements to prevent deficiencies. This guide covers what your healthcare team typically advises, based on NHS clinical practice and how Mounjaro works in your body. Always follow your prescriber's personalised guidance rather than self-supplementing without professional advice.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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.
How Mounjaro Affects Nutrient Absorption
Mounjaro is a GIP and GLP-1 receptor agonist that slows gastric emptying (how quickly food leaves your stomach) and reduces appetite. This means you eat significantly less food, which can impact your intake of key vitamins and minerals. Additionally, reduced stomach acid and slower digestive transit may affect how your body absorbs certain nutrients. Common deficiencies that may develop include vitamin B12, iron, calcium, and folate. Your GP or specialist prescriber should assess your baseline nutritional status before starting Mounjaro and may recommend blood tests to check levels. If you have existing nutritional deficiencies or dietary restrictions (e.g. vegetarian, vegan), inform your prescriber early. The NHS guidance for weight loss medications emphasises monitoring nutritional health throughout treatment, particularly on higher doses of Mounjaro where food intake is most restricted.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Typical Vitamin Supplements Recommended by GPs
Your prescriber may recommend a daily multivitamin as a baseline safeguard, particularly one containing B vitamins (B12, B6, folate) and minerals like iron and calcium. Vitamin B12 is especially important—some patients benefit from B12 injections or high-dose oral supplements if levels drop. Iron supplements are commonly advised for women of reproductive age, as reduced food intake increases deficiency risk. Calcium and vitamin D may be recommended to maintain bone health, particularly for those with limited dairy intake. Always take supplements at least 2–4 hours apart from Mounjaro itself, as the medication may affect absorption timing. Your GP may order follow-up blood tests at 3–6 months and annually thereafter to check nutrient levels. Never start supplements without discussing with your prescriber first—some interact with other medications or may not be necessary for your individual profile.
- 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 vitamins while on Mounjaro?
Possibly, yes. Mounjaro reduces food intake and may affect nutrient absorption, so your GP or specialist may recommend supplements—particularly B vitamins, iron, and calcium. Always ask your prescriber before starting any supplement, as individual needs vary based on your diet, health, and baseline nutrient levels.
Will Mounjaro cause vitamin deficiencies?
Not necessarily, but the risk is higher because you eat less food overall. Regular blood tests can detect early deficiencies. This is why your prescriber monitors your nutritional status throughout treatment and may recommend preventative supplements or dietary adjustments.
Can I take vitamins at the same time as my Mounjaro injection?
No. Space supplements and Mounjaro injections at least 2–4 hours apart, as the medication may affect how your body absorbs oral supplements. Ask your prescriber or pharmacist for the best timing schedule for your specific supplements.
What if I'm vegetarian or vegan on Mounjaro?
Plant-based diets with reduced food intake increase the risk of B12, iron, and calcium deficiencies. Inform your GP or specialist about your diet before starting Mounjaro. They may recommend higher-dose supplements or B12 injections to maintain adequate levels.
How often will my GP check my nutrient levels?
Your prescriber should order baseline blood tests before starting Mounjaro and typically recheck nutrient levels at 3–6 months and annually thereafter. If you experience symptoms like fatigue, shortness of breath, or weak nails, report these to your GP promptly—they may indicate deficiency.
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.