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 Supplements Should You Take With Mounjaro?
When taking Mounjaro (tirzepatide), you may need to adjust your supplement routine because this prescription-only injection affects how your body absorbs nutrients and medication. Since Mounjaro slows gastric emptying—how quickly food moves through your stomach—it can reduce the absorption of some oral supplements. Before adding any supplements, you should discuss your plan with your GP or prescriber. This guide explains what you need to know about supplementation whilst on Mounjaro treatment in the UK.
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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.
How Mounjaro Affects Nutrient Absorption
Mounjaro works by activating GIP and GLP-1 receptors, which slows gastric emptying and helps regulate appetite. This slower digestion means nutrients and medications spend more time in your stomach and less time being absorbed in your intestines. This reduced absorption can affect several types of supplements, particularly vitamins and minerals that rely on stomach acid for absorption, such as B12, iron, and calcium.
- Oral medications and supplements: May be absorbed less effectively when taken at the same time as Mounjaro
- Timing matters: Some supplements may need to be taken at different times than your Mounjaro injection or other medications
- Form matters: Liquid or sublingual supplements may absorb better than tablets during GLP-1 treatment
- Individual variation: How much your absorption is affected depends on your dose, how long you've been taking Mounjaro, and your personal digestive health
Your prescriber can assess whether you need supplement adjustments based on your medical history and current medications.
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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.
Which Supplements Need Special Attention?
Vitamin B12: Mounjaro may reduce B12 absorption from food and oral supplements. If you have a history of B12 deficiency or pernicious anaemia, mention this to your GP—you may need B12 injections instead of oral supplements. Oral contraceptives: If you take the contraceptive pill, you should add a barrier method or switch to a non-oral contraceptive for 4 weeks after starting Mounjaro and after each dose increase, as GLP-1 effects on gastric emptying may reduce oral medication absorption.
Iron and calcium: These minerals are best absorbed in acidic stomach conditions; slowed digestion may reduce their availability. Ask your GP whether you need higher doses or different forms. Always inform your prescriber of all supplements and medications you're taking before starting Mounjaro treatment.
- 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 and supplements with Mounjaro?
Yes, you can take vitamins and supplements with Mounjaro, but timing and form matter. Because Mounjaro slows gastric emptying, some supplements absorb less effectively if taken simultaneously with food or your injection. Discuss your specific supplements with your GP to ensure they're appropriate and properly timed for your individual situation.
Does Mounjaro affect B12 absorption?
Mounjaro may reduce B12 absorption from food and oral supplements due to slower stomach emptying. If you have a history of B12 deficiency or concern, ask your GP about blood tests. They may recommend B12 injections instead of oral supplements, which bypass the absorption issue entirely.
Should I take supplements at a different time than Mounjaro?
Yes, timing can help. Separating oral supplements from your injection day or taking them at different times may improve absorption. However, the best approach depends on the specific supplement. Your prescriber can advise whether spacing out medications and supplements is helpful in your case.
Are there supplements I should avoid on Mounjaro?
There's no blanket list of supplements to avoid, but inform your GP of everything you take. The main concern is reduced absorption of certain vitamins and minerals. Large doses of supplements may also cause stomach upset, which is already a common side effect of Mounjaro. Start conservatively and adjust based on tolerability.
Can I use a weight loss calculator to track results while taking Mounjaro?
Yes—our free GLP-1 weight loss calculator can help you estimate potential weight loss and track your progress on Mounjaro at different doses. Alongside this, use our BMI calculator to monitor your personal BMI throughout treatment. Many people also use our free progress tracker to log weekly weight changes.
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.