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
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Supplements While on Mounjaro — A UK Safety Guide
Taking supplements alongside Mounjaro (tirzepatide) requires careful consideration because this prescription-only injection can affect how your body absorbs certain nutrients and medications. This guide explains which supplements may be safe to use with Mounjaro, why absorption matters, and when to speak with your GP or prescriber. If you're considering Mounjaro as part of a weight management plan, understanding potential supplement interactions is an important part of staying healthy. Always discuss any supplements you take with your prescriber before starting or continuing them alongside 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.
How Mounjaro Affects Nutrient Absorption
Mounjaro (tirzepatide) slows gastric emptying — the rate at which food moves from your stomach into the small intestine. This side effect can affect how your body absorbs nutrients, including vitamins and minerals from supplements. Common concerns include:
- Reduced absorption of fat-soluble vitamins (A, D, E, K) due to slowed fat digestion
- Potential decreased absorption of vitamin B12 and iron — particularly important if you have a history of deficiency
- Changes to how oral medications and supplements dissolve and absorb
- Delayed absorption of certain minerals, including calcium and magnesium
Because Mounjaro may also reduce your overall food intake significantly, your dietary intake of essential nutrients may decrease. This combination means that even if you're taking supplements, absorption may be lower than expected. Your GP or a registered dietitian can assess whether you need additional supplementation or adjusted doses while on Mounjaro, and recommend the mounjaro dose titration schedule to monitor your nutritional status as your dose increases.
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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 May Be Safe to Consider
Some supplements may be appropriate to use with Mounjaro, but always discuss specific products with your prescriber first. Generally considered safer options include:
- Vitamin B12 (especially important if at risk of deficiency)
- Calcium supplements — take separately from other medications and supplements by at least 2 hours
- Vitamin D — often recommended alongside calcium
- Iron supplements (if you have documented deficiency) — take on an empty stomach if possible
- Multivitamins — though absorption may be reduced
However, some supplements can interact negatively with Mounjaro. Avoid high-dose antacids, certain herbal supplements, and products that may affect blood sugar or digestion without prescriber approval. The key principle: spacing matters. If you take supplements, separate them from Mounjaro by at least 30 minutes to 2 hours where possible to maximise absorption. Keep a record of all supplements and medications to share with your GP during check-ups.
- 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?
Multivitamins may be taken, but absorption is likely reduced due to slowed gastric emptying. Discuss with your GP or prescriber about whether you need a prescription-strength multivitamin or if individual supplement dosing would be more effective for you. Space multivitamins at least 30 minutes to 2 hours away from food.
Does Mounjaro affect vitamin B12 absorption?
Yes. Mounjaro can reduce B12 absorption, which is particularly concerning if you're at risk of deficiency. Your prescriber may recommend B12 supplementation or monitoring through blood tests. B12 supplements in sublingual (under-tongue) or injection forms may be absorbed more effectively than oral tablets.
Should I take supplements at a specific time with Mounjaro?
Yes. Take supplements at least 30 minutes to 2 hours away from your Mounjaro injection and from main meals. This spacing helps maximise absorption and reduces the risk of interaction. Ask your pharmacist for personalised timing advice based on your specific supplements.
Will my GP monitor my nutrient levels while I'm on Mounjaro?
Your prescriber should monitor your overall health, but you may need to request specific nutrient testing (B12, iron, calcium, vitamin D). If you're experiencing symptoms of deficiency such as fatigue, weakness, or brittle nails, discuss this with your GP. Regular check-ups are part of safe Mounjaro use.
What supplements should I avoid while taking Mounjaro?
Avoid high-dose antacids, certain weight loss herbs, and supplements affecting blood sugar without prescriber approval. Some herbal products can slow digestion further or interact with Mounjaro's mechanism. Always inform your GP of any supplements, including herbal remedies, before starting Mounjaro.
Ready to take control of your weight loss journey?
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