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 On Mounjaro — What You Need to Know
If you're taking Mounjaro (tirzepatide) and considering supplements, it's important to understand how they interact with your medication. Mounjaro can affect how your body absorbs oral medications and nutrients, which may impact supplement effectiveness. This NHS-aligned guide explains key considerations for safe supplement use alongside Mounjaro, including timing, nutrient deficiencies to watch for, and when to speak to your GP about your specific situation.
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.
How Mounjaro Affects Supplement Absorption
Mounjaro works by slowing gastric emptying — the rate at which food moves from your stomach into your small intestine. This delayed digestion can affect how your body absorbs oral medications and supplements. Supplements taken at the same time as Mounjaro may be absorbed less effectively, which means they might not work as well as intended.
Additionally, Mounjaro can reduce overall appetite and food intake, which may lead to nutritional gaps over time, particularly in:
- Vitamin B12 — important for energy and nerve function
- Iron — especially for women of childbearing age
- Calcium and vitamin D — essential for bone health
- Folate — critical if you might become pregnant
- Vitamin B1 (thiamine) — rarely depleted but worth monitoring
Many people using Mounjaro benefit from a baseline nutritional assessment with their GP or a registered dietitian before starting supplements.
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.
Practical Supplement Guidance While On Mounjaro
Timing is key: Take supplements at least 30 minutes to 1 hour before your Mounjaro injection or several hours after eating. This reduces the risk of reduced absorption. Water-soluble vitamins (B vitamins, vitamin C) are generally safer than fat-soluble vitamins (A, D, E, K) if absorption is a concern.
If you're considering vitamin D, calcium, iron, or B12 supplements, discuss with your GP first — they may recommend a blood test to check your current levels. Some people on Mounjaro benefit from intramuscular B12 injections rather than oral supplements, as they bypass absorption issues entirely. Never stop taking essential medications or supplements without consulting your prescriber.
- 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?
Yes, but timing matters. Take multivitamins at least 30 minutes before your Mounjaro injection or several hours after eating to maximise absorption. Discuss with your GP first — they may recommend specific supplements based on your individual nutritional needs and blood work.
Will Mounjaro affect my oral contraceptive?
Yes, Mounjaro can reduce absorption of oral contraceptives. The NHS and MHRA recommend adding a barrier method (condom) or switching to a non-oral contraceptive for 4 weeks after starting Mounjaro and 4 weeks after each dose increase to ensure reliable contraception.
Should I take a vitamin B12 supplement on Mounjaro?
Many people on Mounjaro benefit from B12 monitoring. Your GP can arrange a blood test to check your level. Intramuscular B12 injections often work better than oral supplements because they bypass absorption issues. Discuss with your GP before starting any B12 supplement.
What nutrients am I at risk of deficiency with?
The main concerns are B12, iron, calcium, vitamin D, and folate. These deficiencies can develop because Mounjaro reduces food intake and may affect nutrient absorption. A GP or registered dietitian can assess your individual risk and recommend appropriate testing or supplementation.
Is it safe to take herbal or natural supplements on Mounjaro?
Some herbal supplements can interact with Mounjaro or affect its absorption. Always inform your GP or prescriber about any herbal remedies, vitamins, or supplements you're taking — they can advise whether they're safe to use alongside your tirzepatide.
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.