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 I Take With Mounjaro?
If you're taking Mounjaro (tirzepatide) for weight management in the UK, you may wonder whether supplements are safe or necessary. The short answer is: some supplements may be beneficial, but many require careful timing and discussion with your GP. Mounjaro can affect how your body absorbs nutrients and medications, so supplementation strategy matters. This guide explains what you should know about taking supplements safely with Mounjaro.
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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 Consider With Mounjaro
Mounjaro slows gastric emptying — how quickly food leaves your stomach — which can affect nutrient absorption. Additionally, reduced food intake means you may consume fewer calories and micronutrients overall. Vitamin B12 is particularly important because Mounjaro reduces stomach acid, which aids B12 absorption. Many people taking GLP-1 medications report improved energy levels with B12 supplementation.
- Multivitamin: A general multivitamin (taken at least 2 hours away from Mounjaro injection) may help cover nutritional gaps from reduced food intake. Choose one containing iron, calcium, and B vitamins.
- Vitamin D: UK adults often have low vitamin D. Mounjaro doesn't directly affect vitamin D absorption, but supporting bone health during weight loss is important.
- Calcium: Weight loss can accelerate calcium loss from bone. A supplement alongside dietary sources (dairy, leafy greens) may be protective.
- Fibre supplements: Mounjaro frequently causes constipation. Gradual fibre supplementation (psyllium husk, inulin) can help, but increase slowly to avoid worsening digestive symptoms.
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.
What NOT to Take and Important Timing Rules
Never take oral contraceptives within 4 hours of supplementing with anything that slows stomach transit — Mounjaro itself reduces absorption of oral medications, and additional supplements can compound this. Always separate supplements from Mounjaro injections by at least 2 hours, preferably longer.
- Avoid: Fat-soluble vitamins (A, D, E, K) in large supplemental doses — Mounjaro reduces fat absorption, so excess supplements can accumulate in your body.
- Iron supplements: Avoid unless you have diagnosed iron-deficiency anaemia — excess iron causes constipation and can interfere with other medications.
- Herbal products: Avoid supplements claiming to "boost metabolism" or "enhance weight loss" — these often contain stimulants that may interact unpredictably with tirzepatide.
Your GP or the prescriber managing your Mounjaro treatment should review all supplements before you start them. This is especially important if you're also taking diabetes medications or other prescriptions.
- 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 whilst taking Mounjaro?
Yes, but timing matters. Take your multivitamin at least 2 hours away from your weekly Mounjaro injection — morning dose with breakfast, injection in the evening, or vice versa. This separation helps ensure your body absorbs the multivitamin properly, since Mounjaro slows stomach emptying and can reduce absorption of oral medications.
Does Mounjaro cause vitamin deficiencies?
Mounjaro can increase the risk of certain deficiencies because it reduces stomach acid (affecting B12 absorption) and slows food passage through your digestive system. Additionally, eating less food means fewer nutrients overall. B12 supplementation is often recommended. Mention any deficiency concerns to your GP.
Should I take fibre supplements with Mounjaro?
Fibre supplements may help because Mounjaro commonly causes constipation. However, increase fibre gradually — too much too quickly worsens digestive symptoms. Start with one small dose every few days, taken separately from your Mounjaro injection. Drink plenty of water. Ask your GP for specific recommendations.
Can supplements affect how well Mounjaro works?
Some supplements may reduce Mounjaro's effectiveness by affecting nutrient or medication absorption. Avoid supplements claiming to boost metabolism or enhance weight loss, as these often contain stimulants that may interact unpredictably with tirzepatide. Always inform your prescriber of all supplements.
What should I do before starting any new supplement?
Always speak to your GP or the healthcare professional managing your Mounjaro treatment before starting any new supplement, including vitamins, minerals, or herbal products. They can review your individual health, check for interactions with Mounjaro and any other medications you take, and advise on timing and dosage.
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.