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
Can You Take Supplements While On Mounjaro?
Taking supplements while on Mounjaro (tirzepatide) requires careful consideration, as the medication affects how your digestive system works and may interfere with certain supplements. Because Mounjaro slows gastric emptying — the rate at which food leaves your stomach — it can impact nutrient absorption and the effectiveness of oral medications and supplements. This guide explains which supplements are generally considered safe, which to avoid, and why speaking to your GP or prescriber before starting any new supplement is essential. Most people can safely take certain vitamins and minerals, but timing and type matter significantly.
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?
Many standard vitamins and minerals can be taken alongside Mounjaro, though individual circumstances vary. Safe options typically include:
- Vitamin B12: Often recommended, as GLP-1 and GIP/GLP-1 medications may slightly reduce B12 absorption. Taking B12 supplements or receiving B12 injections is common with tirzepatide.
- Iron supplements: Generally safe but should be separated from Mounjaro injections by at least a few hours, as timing can affect absorption.
- Calcium and vitamin D: Usually compatible, though calcium-rich foods are often preferred over supplements when experiencing nausea.
- Magnesium: May help with constipation, a common side effect of Mounjaro, though your prescriber should advise on dose.
- Electrolyte supplements: Useful if you're experiencing diarrhoea or vomiting from Mounjaro's initial side effects.
Always inform your prescriber of any supplements you're taking — they can assess compatibility with your personal health profile and current medications.
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 Avoid or Use With Caution
Certain supplements and products require caution or should be avoided: Fat-soluble vitamins (A, D, E, K) in high doses may be less effectively absorbed due to Mounjaro's effects on digestion, though normal dietary amounts are fine. Weight loss supplements containing stimulants (caffeine, synephrine) may cause unwanted side effects when combined with appetite suppression. Herbal supplements like St John's Wort can interfere with medication absorption. Digestive enzyme supplements may not be necessary and could complicate your treatment. Always discuss new supplements with your GP before starting them. Your prescriber can review interactions specific to your tirzepatide dose, any other medications, and your health conditions. This is particularly important if you're taking diabetes medications or have any underlying health concerns.
- 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 multivitamins while on Mounjaro?
Most standard multivitamins are safe to take with Mounjaro, but timing matters. Take them at a different time of day from your injection, ideally with food. Some people find multivitamins easier to tolerate as a liquid or chewable form if nausea is an issue. Always check with your prescriber first, as individual circumstances vary.
Does Mounjaro affect vitamin absorption?
Yes, tirzepatide may slightly affect how your body absorbs certain nutrients because it slows gastric emptying and reduces appetite. This is why B12 supplementation is often recommended. Your GP may suggest blood tests to check your nutrient levels during treatment, particularly if you're on Mounjaro long-term.
Is it safe to take fibre supplements on Mounjaro?
Fibre supplements can be helpful for constipation, a common Mounjaro side effect, but introduce them gradually and drink plenty of water. Too much fibre too quickly can worsen digestive issues. Your prescriber can recommend a safe approach that works with your individual response to the medication.
Can I take weight loss supplements alongside Mounjaro?
This is not recommended. Mounjaro itself is a prescription weight loss medication, and adding other weight loss supplements increases the risk of side effects and unpredictable interactions. Stick with what your prescriber recommends. Focus on lifestyle changes — diet and physical activity — alongside your tirzepatide treatment.
Should I tell my GP about supplements I'm already taking?
Yes, absolutely. Always inform your GP or prescriber about any vitamins, minerals, herbal products, or over-the-counter supplements before starting Mounjaro or adjusting doses. Some supplements can interact with tirzepatide or affect its absorption, so a full picture of what you're taking is essential for safe treatment.
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.