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 When On Mounjaro?
If you're considering Mounjaro (tirzepatide) or already taking it, you may wonder whether supplements are safe to use alongside this prescription weight management injection. The short answer is that some supplements may interact with Mounjaro, whilst others are generally safe — but individual circumstances vary. Your prescriber and GP should always assess your specific supplement use before you start Mounjaro, and you should inform them of everything you're taking. This guide explains the key considerations for UK adults using Mounjaro with supplements.
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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 Supplements to Discuss With Your Prescriber
Before starting Mounjaro, tell your prescriber about all supplements, vitamins, and herbal products you take — including vitamin D, calcium, iron, B vitamins, and any herbal remedies. Some supplements may have reduced absorption when taking Mounjaro because the injection slows how quickly food moves through your stomach (gastric emptying). Oral contraceptives are particularly important to discuss: Mounjaro may reduce their effectiveness, so you may need to use additional contraception for 4 weeks after starting and 4 weeks after each dose increase. Fat-soluble vitamins (A, D, E, K) may also be affected by slowed digestion. If you have a medical condition requiring specific supplementation — such as vitamin B12 injections for pernicious anaemia, or iron supplementation for anaemia — your GP may need to monitor levels more closely or adjust timing of supplements. Always bring a complete list to your appointment, including over-the-counter products and herbal supplements you use regularly. Your prescriber will assess whether any adjustments are needed and may recommend spacing supplements and Mounjaro injections apart by a certain time period.
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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.
When to Seek GP Advice About Supplements
If you're already taking Mounjaro and want to start a new supplement, or if you notice any unusual side effects after beginning a new supplement, contact your GP or the NHS specialist weight management service where you're being a UK pharmacy. Some warning signs include persistent nausea beyond normal Mounjaro side effects, unexplained fatigue, changes in your digestion, or signs of nutritional deficiency. Because Mounjaro affects how your body absorbs nutrients, your GP may recommend periodic blood tests to check vitamin and mineral levels — this is particularly important if you've been on Mounjaro for several months or are taking high doses. If you're considering stopping Mounjaro to take a supplement your prescriber has advised against, discuss alternatives with your GP first rather than stopping treatment without guidance. Many supplements have safer alternatives, and your prescriber can help you find options that work with your treatment plan.
- 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 vitamin supplements with Mounjaro?
Many vitamin supplements are safe with Mounjaro, but timing and type matter. Fat-soluble vitamins (A, D, E, K) may have reduced absorption due to slower stomach emptying. Your GP or prescriber can advise on dosing, timing, and whether blood tests are needed to monitor levels. Always inform them before starting any supplement.
Will Mounjaro reduce the effectiveness of my oral contraceptive?
Yes, Mounjaro may reduce oral contraceptive absorption. The MHRA guidance recommends using additional contraception (barrier methods or non-oral alternatives) for 4 weeks after starting Mounjaro and 4 weeks after each dose increase. Discuss contraception options with your prescriber before starting treatment.
Should I take supplements at the same time as my Mounjaro injection?
No. Most supplements should be taken several hours apart from your Mounjaro injection to maximise absorption. Your GP or prescriber can advise on exact timing based on your specific supplements and medical history. Never adjust timing without professional guidance.
Can I take herbal supplements with Mounjaro?
Some herbal supplements may interact with Mounjaro or be affected by reduced nutrient absorption. Herbal remedies like ginger (for nausea) or milk thistle should be discussed with your prescriber first. Many herbal products are not well-studied in combination with GLP-1 or GIP/GLP-1 agonists, so caution is advised.
What if I'm deficient in vitamin B12 or iron whilst on Mounjaro?
Tell your prescriber immediately. Mounjaro may affect B12 and iron absorption, so your GP may recommend injections, sublingual supplements, or adjusted dosing. Blood tests can confirm deficiency levels. Your healthcare team will create a plan to address deficiency safely whilst continuing Mounjaro.
Ready to take control of your weight loss journey?
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