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) is possible, but you need to be aware of potential interactions and how this dual GIP and GLP-1 receptor agonist affects nutrient absorption. Because Mounjaro slows how quickly food moves through your stomach, it can affect how your body absorbs certain vitamins and minerals—including supplements. This guide explains which supplements may be safe, which to avoid, and what to discuss with your GP before starting any new supplement while 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 slowing gastric emptying—the rate at which food leaves your stomach. While this effect typically reduces over time, it can initially affect how your body absorbs nutrients from food and supplements. Water-soluble vitamins (B vitamins, vitamin C) and minerals (iron, calcium) may be absorbed less efficiently when the tirzepatide dose is higher or when you've just started treatment.
This is why many people on GLP-1 medications like Wegovy, or dual GIP/GLP-1 medications like Mounjaro, are advised to take a multivitamin supplement to cover potential gaps. However, the timing and type of supplement matter significantly. A prescriber assessing your individual health may recommend specific supplements based on your diet, existing deficiencies, or medical history.
- B12 supplements may be especially important if you're not eating enough meat or fortified foods
- Iron supplements should be taken separately from calcium (they compete for absorption)
- Fat-soluble vitamins (A, D, E, K) require dietary fat for absorption—take with food when on Mounjaro
Clinically BackedWeight Loss
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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.
Supplements To Avoid Or Use Cautiously On Mounjaro
Certain supplements can interact with Mounjaro or worsen side effects. Oral contraceptives have reduced absorption on Mounjaro—if you take the pill, your GP may recommend a barrier method or alternative contraception for 4 weeks after starting and after each dose increase. This is critical for contraceptive reliability.
Supplements containing high doses of fibre may increase bloating, nausea, or constipation—side effects already common on Mounjaro. Herbal supplements claiming to regulate blood sugar (such as chromium or alpha-lipoic acid) may interact unpredictably if you have diabetes.
Always inform your prescriber of all supplements you're taking, including herbal remedies, omega-3, probiotics, or weight loss supplements. Some weight loss products contain stimulants that may not be safe with Mounjaro. Your GP or prescriber can assess individual safety for your health profile.
- 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 while on Mounjaro?
Yes, a standard multivitamin is often recommended while taking Mounjaro because the medication may reduce nutrient absorption. However, timing matters—take it with food, and separate it from other supplements that may compete for absorption. Discuss specific supplement choices with your GP or prescriber before starting.
Does Mounjaro affect iron or B12 absorption?
Yes, Mounjaro may reduce absorption of B12 and iron because it slows stomach emptying. If you're at risk of deficiency (vegetarian, vegan, or with existing B12 issues), your prescriber may recommend supplementation. B12 injections or sublingual supplements bypass the stomach and may be more reliable.
Can I take weight loss supplements alongside Mounjaro?
No—taking additional weight loss supplements alongside Mounjaro is not recommended without prescriber approval. Some products contain stimulants or ingredients that may interact with tirzepatide or worsen side effects. Always check with your GP before adding any weight loss product.
Should I take supplements at a different time of day on Mounjaro?
Yes. Take supplements with or just after meals to improve absorption. Avoid taking them on an empty stomach—the slowed digestion from Mounjaro means absorption will be poor. Separate iron and calcium supplements by at least 2 hours, as they compete for absorption.
Can I use probiotics while taking Mounjaro?
Probiotics are generally considered safe on Mounjaro, and some people find them helpful for digestive side effects. However, evidence for their effectiveness is mixed. Start with a standard probiotic and monitor how you feel. If side effects worsen, stop and inform your GP.
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.