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 Multivitamins With Mounjaro?
When taking Mounjaro (tirzepatide) for weight management, many people wonder whether it's safe to take multivitamins alongside their injections. Mounjaro may affect how your digestive system absorbs certain nutrients, particularly because it slows gastric emptying—how quickly food moves from your stomach. This is an important consideration for long-term health. Your GP or prescriber should always be consulted before starting any new supplement while on Mounjaro, as they can assess your individual nutritional needs and medication interactions.
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 Nutrient Absorption
Mounjaro is a dual GIP and GLP-1 receptor agonist that works by slowing how quickly food leaves your stomach and reducing appetite. This delayed gastric emptying means nutrients from food may be absorbed differently than usual. Early in treatment, when you're taking smaller doses, this effect is more pronounced. As your body adapts over weeks, gastric emptying typically returns closer to normal, though appetite suppression continues.
Because Mounjaro reduces overall food intake and may affect nutrient absorption timing, some people experience reduced intake of essential vitamins and minerals—particularly vitamin B12, iron, and calcium. Research on GLP-1 medications suggests that long-term use may lower B12 levels in some users, though this is not universal.
- B12 deficiency risk is higher if you have reduced food intake or existing absorption issues
- Iron absorption can be affected by reduced stomach acid and slower digestion
- Calcium absorption may be compromised if gastric pH changes
Before starting supplementation, ask your prescriber whether blood tests are needed to identify any actual deficiencies rather than supplementing unnecessarily.
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.
Safe Supplementation While on Mounjaro
If your GP confirms you need supplementation, timing and form matter. Take multivitamins or individual supplements at least 4 hours away from your Mounjaro injection day if possible, as the injection's effects on gastric emptying are strongest immediately after injection. Liquid or chewable supplements may be absorbed better than tablets when taking Mounjaro, since they require less digestive effort.
Oral contraceptives have a specific warning with Mounjaro—they may be less effective due to reduced absorption—so using a barrier method for 4 weeks after starting and after each dose increase is recommended. This same principle applies to some other oral medications. Always inform your prescriber of all supplements and medications, including over-the-counter vitamins, herbal remedies, and minerals. Your prescriber or a registered dietitian can recommend appropriate forms and doses for your situation. Regular blood tests can monitor whether supplementation is working.
- 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 with my Mounjaro injection?
Yes, you can take multivitamins while on Mounjaro, but timing and form matter. Take supplements at least 4 hours away from your injection day when possible, use liquid or chewable forms if tolerated, and always inform your prescriber. Blood tests can confirm whether you actually need supplementation before starting.
Does Mounjaro cause vitamin deficiency?
Mounjaro may reduce nutrient absorption and food intake, particularly affecting B12, iron, and calcium. However, not everyone develops deficiencies. Your GP can arrange blood tests to identify actual deficiencies rather than guessing. This is especially important if you have reduced appetite or existing digestive conditions.
Should I take supplements on the day of my Mounjaro injection?
It's best to avoid taking supplements on your injection day if possible, as Mounjaro's effect on gastric emptying is strongest immediately after injection. Space supplements at least 4 hours from injection time. However, your prescriber may recommend different timing based on your individual needs.
What's the difference between Mounjaro and Wegovy regarding supplements?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are GLP-1-type medications that slow gastric emptying and may affect nutrient absorption. Mounjaro has a slightly stronger effect due to its dual GIP and GLP-1 mechanism. Supplement recommendations are similar for both—discuss with your prescriber before starting anything new.
Can multivitamins interact with tirzepatide medication?
Direct interactions between most standard multivitamins and tirzepatide are rare. The main concern is reduced absorption rather than a chemical interaction. However, always tell your prescriber about all supplements, as some may affect digestion or blood sugar differently when taking Mounjaro.
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.