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
Best Vitamins When Taking Mounjaro
When taking Mounjaro (tirzepatide), your body's nutritional needs may change due to reduced food intake and changes in how your digestive system works. Whilst Mounjaro is a prescription-only weight management injection available through NHS specialist services or private prescribing in the UK, it's important to understand potential vitamin and mineral deficiencies. Your GP or prescriber should discuss nutritional support as part of your overall treatment plan, particularly if you're experiencing reduced appetite or gastrointestinal side effects.
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.
Nutritional Considerations With Mounjaro Treatment
Mounjaro works by activating GIP and GLP-1 receptor pathways, which can significantly reduce appetite and food intake. This reduction in calories is beneficial for weight loss, but it may also mean you consume fewer nutrients from food. Additionally, Mounjaro can slow gastric emptying (how quickly food leaves your stomach), which may temporarily affect nutrient absorption.
- Vitamin B12 — Often depleted with reduced food intake; intrinsic factor changes may reduce absorption even without medication
- Iron — Particularly important for women; reduced dietary intake combined with slower digestion may lower stores
- Calcium and Vitamin D — Critical for bone health; deficiency risk increases with prolonged low-calorie intake
- Folate (B9) — Essential for cell division; reduced intake from fewer vegetables and grains
- Electrolytes (sodium, potassium) — Loss risk with gastrointestinal side effects like diarrhoea or vomiting
Your prescriber or GP should assess your baseline nutritional status before starting tirzepatide and periodically during treatment.
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.
When to Discuss Supplements With Your Healthcare Team
Always consult your GP or prescriber before starting any new supplement or vitamin whilst on Mounjaro. Some vitamins and minerals interact with medications or may not absorb properly if taken at the same time. Your healthcare team can arrange blood tests to check for deficiencies — particularly B12, iron, folate, and vitamin D — and recommend supplementation only if needed.
If you're experiencing persistent nausea, vomiting, or diarrhoea, inform your prescriber immediately, as these side effects can increase nutrient loss. A referral to a registered dietitian through the NHS may be available depending on your region, and private nutritional support is also an option. Don't rely on self-diagnosis — personalised advice based on your blood work is far more effective than general supplementation.
- 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.
Do I need to take vitamins whilst on Mounjaro?
Not necessarily — it depends on your individual diet, nutrient intake, and blood work. Some people maintain adequate nutrition with careful food choices, whilst others develop deficiencies due to reduced appetite or side effects. Your GP or prescriber should check your baseline nutritional status and recommend supplements only if blood tests show a deficiency.
Can I take vitamins at the same time as my Mounjaro injection?
Mounjaro is an injection, not an oral medication, so there's no direct interaction with the injection itself. However, if you take oral vitamin supplements, discuss timing with your prescriber — some vitamins absorb better on an empty stomach, whilst others require food. Spacing them appropriately may improve absorption.
Will Mounjaro affect my ability to absorb vitamins from food?
Mounjaro may slightly affect nutrient absorption by slowing gastric emptying and reducing overall food intake. The impact is usually modest, but individuals with significant gastrointestinal side effects (diarrhoea, vomiting) may experience greater nutrient loss. Your GP can monitor this with blood tests.
Is B12 supplementation necessary on Mounjaro?
B12 deficiency is a common concern with reduced food intake and can develop over time. Whilst not everyone needs supplementation, your GP should check your B12 levels at baseline and during treatment. If deficient, supplementation — either oral, sublingual, or injected — may be recommended depending on severity.
Can I use our BMI calculator to track if my weight loss is healthy whilst on Mounjaro?
Yes — our free BMI calculator can help you track your weight loss progress and ensure your BMI remains in a healthy range. Combined with our progress tracker, you can monitor your journey and share results with your GP to ensure your Mounjaro treatment is working safely alongside proper nutrition.
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.