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 Supplements Should You Take With Mounjaro?
When taking Mounjaro (tirzepatide), many people wonder whether supplements are necessary or safe. The answer depends on your individual health, diet, and what Mounjaro does to your body. This guide explains how Mounjaro affects nutrient absorption, which supplements may be worth considering, and when to speak to your GP. Always consult your prescriber before starting any new supplement alongside your Mounjaro KwikPen prescription, as some may interact with your medication or reduce its effectiveness.
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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 works by slowing gastric emptying — the rate at which food moves through your stomach — and reducing your appetite. This means you eat less food overall. Reduced food intake can lead to lower intake of key nutrients including B vitamins, iron, calcium, and protein, even if you eat a balanced diet.
Additionally, many people on Mounjaro experience nausea, vomiting, or diarrhoea, especially during dose titration (when increasing your dose step by step). These side effects can further affect nutrient absorption and intake. Your GP or the specialist prescribing your tirzepatide should monitor your nutritional status during treatment.
- B vitamins (especially B12): Reduced food intake and potential stomach issues may lower B12 levels over time — important for energy and nerve function
- Iron: Less stomach acid and reduced intake may affect iron absorption — particularly relevant for women
- Calcium: Essential for bone health; reduced dairy intake while on Mounjaro could be a concern long-term
- Protein: Critical to preserve muscle mass during weight loss — many people struggle to eat enough protein on GLP-1 medication
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.
Supplements Worth Discussing With Your GP
Before starting any supplement, discuss it with your prescriber or GP. They can assess whether you specifically need supplementation based on your blood work and diet. Some supplements commonly considered by people on weight loss medications include:
- B12 supplement or injections: Especially if you're vegetarian, vegan, or experiencing reduced food intake long-term
- Multivitamin: A general multivitamin may help cover nutritional gaps, but should be taken separately from Mounjaro (see interaction notes below)
- Protein powder: Not a supplement but worth mentioning — helps meet protein goals when appetite is reduced
- Iron supplement: Only if blood tests show low iron; excess iron can be harmful
- Calcium with vitamin D: For bone health, particularly important during sustained weight loss
Your NHS specialist weight management service can arrange blood tests to check your nutrient levels and guide personalised supplementation.
- 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 while on Mounjaro?
Yes, but timing matters. Take oral vitamins at least 1–2 hours before or after your Mounjaro dose, as Mounjaro slows stomach emptying and may reduce how well oral medications and supplements are absorbed. Liquid vitamins or injections (like B12 injections) avoid this interaction. Always check with your GP first.
Does Mounjaro cause vitamin deficiencies?
Not directly, but reduced food intake while on tirzepatide can lead to lower overall nutrient intake. Side effects like nausea and diarrhoea may also affect absorption. Your prescriber can arrange blood tests to check your nutrient levels and advise on supplementation if needed.
Is protein supplementation necessary on Mounjaro?
Not always, but it can be helpful. Many people struggle to eat enough protein while on Mounjaro due to reduced appetite. Adequate protein is important to preserve muscle mass during weight loss. A protein shake or powder can help you meet your goals without adding bulk to your diet.
Can supplements interfere with how Mounjaro works?
Some may. Mounjaro slows stomach emptying, which affects how quickly oral supplements and medications are absorbed. This can reduce their effectiveness. Fat-soluble vitamins (A, D, E, K) may be affected more than water-soluble ones. Always inform your prescriber of all supplements before starting them.
Should I take supplements if I'm losing weight on Mounjaro?
Weight loss itself doesn't automatically require supplements, but reduced calorie intake does mean fewer nutrients overall. Your GP may recommend blood tests to check for deficiencies, particularly after several months on Mounjaro, and then guide supplementation based on your individual results.
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.