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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What Supplements Should You Take While on Mounjaro?
When taking Mounjaro (tirzepatide), your body's nutrient absorption and dietary intake change significantly due to reduced appetite and altered digestion. This means certain supplements and vitamins may become more important to maintain your health. This guide covers which supplements are worth considering whilst on Mounjaro, how they interact with the medication, and what to discuss with your GP or prescriber before adding anything new to your routine. Always consult your prescriber before starting any new supplement.
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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 Nutrient Gaps While Taking Mounjaro
Mounjaro works by reducing appetite and slowing how quickly food leaves your stomach, which can lead to significantly lower food intake. This dietary restriction may create gaps in essential nutrients, particularly if your reduced appetite makes it harder to eat balanced meals. Vitamin B12 is commonly deficient in people on weight loss medications — your body absorbs less from food, and reduced overall intake compounds this. Iron, calcium, and vitamin D are also at risk, especially if you're eating fewer dairy products or iron-rich foods. Additionally, reduced food volume means fewer essential amino acids and minerals. Your GP can request blood tests to check your baseline nutrient levels before starting Mounjaro or after a few months of treatment. This helps identify which supplements are genuinely needed rather than taking everything speculatively, which wastes money and may cause interactions.
- B12 — critical for energy and nerve function; absorption reduced on Mounjaro
- Iron — easier to become deficient with lower food intake
- Calcium and Vitamin D — essential for bone health during weight loss
- Magnesium — supports digestion and may help with side effects
- Omega-3 fatty acids — harder to obtain from reduced fish and oil intake
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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 Discuss With Your Prescriber
Before adding any supplement whilst on Mounjaro, always discuss it with your GP or the prescriber who issued your tirzepatide prescription. Some supplements interact with medications or affect how quickly Mounjaro works. Oral contraceptives are particularly important — Mounjaro slows stomach emptying, which reduces absorption of birth control pills; your prescriber may recommend barrier methods or a different contraceptive for 4 weeks after starting and after each dose increase. Supplements containing iron or calcium should be taken separately from other medications, as they can reduce absorption. Fat-soluble vitamins (A, D, E, K) are best absorbed with food, which may be challenging with reduced appetite. A simple blood test can confirm which supplements you actually need, rather than guessing.
- 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.
Is it safe to take multivitamins while on Mounjaro?
Yes, a standard multivitamin is generally safe with Mounjaro, but check with your prescriber first. Avoid megadoses of any single nutrient. Some multivitamins contain fillers that may upset your stomach on Mounjaro — choose a gentle formulation. A blood test can identify which specific nutrients you actually lack, allowing you to supplement only what you need.
Should I take B12 supplements on Mounjaro?
Many people on Mounjaro benefit from B12 supplementation because reduced food intake and slower stomach emptying impair natural absorption. Ask your GP for a baseline B12 test before starting Mounjaro. If levels are borderline or low, your GP may recommend B12 injections (more reliable than tablets) or sublingual supplements, which bypass stomach absorption entirely.
Will supplements help with Mounjaro side effects like nausea?
Some supplements may help — ginger and peppermint are traditionally used for nausea, though evidence is modest. Magnesium supplements sometimes ease constipation, a common Mounjaro side effect. However, never use supplements to self-treat serious side effects; always contact your GP or prescriber if side effects persist or worsen. Your prescriber may adjust your dose or recommend specific remedies.
Can I take supplements that slow digestion while on Mounjaro?
Avoid fibre supplements or high-dose magnesium without medical guidance — Mounjaro already slows digestion, and adding more may worsen constipation or cause discomfort. However, gentle soluble fibre (psyllium husk) taken with plenty of water may actually help manage side effects. Discuss specific products with your GP before starting. Use our free progress tracker to monitor how your body responds to any changes.
What about protein supplements or shakes on Mounjaro?
Protein shakes can be helpful because reduced appetite makes it harder to eat enough whole protein. Choose a gentle, easy-to-digest shake that won't upset your stomach — many people on Mounjaro struggle with heavy, sweet drinks. Check with your prescriber, but most protein supplements are safe. Shakes are particularly useful if nausea prevents you from eating solid meals.
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.