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
Supplements While On Mounjaro — What's Safe?
Taking supplements alongside Mounjaro (tirzepatide) is common, but it's important to understand which ones are safe and which may interact with your prescription. Mounjaro is a GIP and GLP-1 receptor agonist that affects how your stomach absorbs nutrients and medications, which means some supplements may not work as intended or could potentially cause problems. Your GP or prescriber should always review your complete supplement list before you start Mounjaro, and they can advise whether your current routine needs adjusting.
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.
Which Supplements Are Generally Safe With Mounjaro?
Most common vitamins and minerals are safe to take alongside Mounjaro, but timing and absorption are key. Because Mounjaro slows how quickly food (and medications) move through your stomach, taking supplements at the same time as your injection may reduce their effectiveness. The safest approach is to separate supplements from your Mounjaro dose by at least 2–4 hours.
- Vitamin B12: Often recommended for Mounjaro users due to reduced appetite and potential dietary gaps — safe and commonly advised by GPs
- Vitamin D: Safe to take; particularly important as excess weight is linked to lower vitamin D levels
- Calcium: Generally safe but separate from any iron or certain medications
- Multivitamins: Fine if taken separately from your injection, preferably at a different meal
- Probiotics: No established interaction with Mounjaro, though evidence for weight loss is limited
Always inform your GP or pharmacist before starting any new supplement, especially if you're also taking diabetes medications or other prescriptions.
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 to Discuss With Your Prescriber
Some supplements require caution or may need timing adjustment when using Mounjaro. Iron supplements should be taken separately as Mounjaro may affect absorption — typically 2+ hours apart. Calcium supplements can interfere with iron, so these also need spacing. If you're taking blood pressure or blood sugar medications alongside supplements, your prescriber needs to know the full picture because weight loss itself often improves these conditions.
Herbal supplements such as chromium, berberine, or bitter melon are sometimes used for blood sugar support, but there's limited evidence for their benefit with GLP-1 medicines like tirzepatide. Discuss any herbal or traditional supplements with your GP before starting Mounjaro, as some may interact with your prescription or duplicate its effects.
- 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 a multivitamin with my Mounjaro injection?
Yes, but avoid taking it at the same time. Mounjaro slows gastric emptying, which can reduce how well supplements are absorbed. Take your multivitamin at a different meal, preferably 2–4 hours away from your injection, and your prescriber can advise on the best timing for your routine.
Is vitamin B12 safe to take with Mounjaro?
Yes. In fact, GPs often recommend B12 supplementation for Mounjaro users because reduced appetite may lead to lower intake of B12-rich foods. B12 is water-soluble and generally very safe. Take it separately from your injection for best absorption, and discuss dosing with your GP or pharmacist.
Will supplements affect how well Mounjaro works?
Most supplements won't reduce Mounjaro's effectiveness, but some may not work as well if taken together. Separation is the key — take supplements at least 2–4 hours away from your Mounjaro dose. Your prescriber can advise on your specific supplements and the best schedule.
Should I tell my GP about all my supplements before starting Mounjaro?
Absolutely, yes. Always provide a complete list of supplements, herbs, and over-the-counter products. Some supplements interact with Mounjaro, diabetes medications, or blood pressure drugs. Your GP or pharmacist can then advise which are safe and how to space them optimally.
Are there supplements that could interact with tirzepatide?
While serious interactions are rare, some herbal products (such as chromium or berberine) may have overlapping effects with Mounjaro's blood sugar action. St. John's Wort can affect medication absorption. Always discuss herbal or weight-loss supplements with your prescriber — they'll assess safety based on your full medical history and current medications.
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.