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
What Supplements Can You Take Safely With Mounjaro?
If you're taking Mounjaro (tirzepatide) for weight management, you may wonder whether supplements are safe to use alongside your medication. Because Mounjaro slows gastric emptying and may affect how your body absorbs certain nutrients, choosing the right supplements — and discussing them with your GP or prescriber — is important. This guide covers what you need to know about supplementation whilst using this GLP-1 and GIP receptor agonist injection in the UK.
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.
Key Nutrient Considerations With Mounjaro
Mounjaro works by slowing how quickly food moves through your stomach, which can initially reduce appetite and food intake. Over time, this effect may decrease, but in the early stages, some people eat considerably less food, which may affect nutrient intake. Common nutritional concerns include:
- B vitamins (especially B12): Reduced food intake and slower gastric transit may lower B12 absorption. B12 supplements or injections may be recommended by your GP, particularly if you have existing risk factors.
- Iron: Similar absorption concerns apply, especially for women of reproductive age. Iron supplements may be needed, though timing matters — iron should be taken separately from other medications.
- Calcium and vitamin D: Essential for bone health, particularly important during sustained weight loss. Your GP may recommend supplementation.
- Electrolytes: If nausea or diarrhoea occurs (common Mounjaro side effects), electrolyte balance matters. Plain water is usually sufficient, but your prescriber may advise electrolyte support.
The best approach is to discuss any nutritional concerns with your GP or specialist before starting supplementation.
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.
Mounjaro vs Wegovy: Supplement Needs and Absorption
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are GLP-1-based weight loss injections licensed in the UK, and both slow gastric emptying — meaning both may affect nutrient absorption similarly. However, Mounjaro's dual GIP and GLP-1 mechanism may affect appetite and food intake slightly differently than Wegovy's single GLP-1 pathway. In clinical trials, Mounjaro showed average weight loss of around 20.9% at maximum dose, whilst Wegovy showed approximately 14.9%. This difference in weight loss magnitude might theoretically affect nutritional needs differently, though individual variation is significant. Regardless of which medication you use, the same principles apply: monitor your nutrient intake, discuss supplements with your prescriber, and use our free GLP-1 weight loss calculator to understand your personal weight loss projection and nutritional support needs.
Always inform your prescriber of any supplements you're taking, as some may interact with Mounjaro or affect medication absorption. Oral contraceptives, for example, may have reduced effectiveness due to slower gastric emptying — your prescriber will advise on this. Fat-soluble vitamins (A, D, E, K) may also be affected by Mounjaro's impact on fat digestion. Your GP can assess whether you need specific supplementation based on your individual health, diet, and weight loss rate. Never start supplements without mentioning them to your prescriber, even if they seem "natural" or over-the-counter.
- 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?
Yes, multivitamins are generally safe whilst taking Mounjaro, but discuss the brand and timing with your GP first. Some multivitamins contain iron or calcium, which should be taken separately from other medications due to absorption timing. Your prescriber may recommend a specific formulation or timing schedule based on your individual needs.
Should I take B12 supplements with Mounjaro?
Many people taking Mounjaro benefit from B12 supplementation, particularly if they experience reduced food intake. B12 injections or high-dose oral supplements are common recommendations. Ask your GP whether B12 monitoring or supplementation is appropriate for you, especially if you have existing risk factors like pernicious anaemia or dietary restrictions.
Is it safe to take supplements alongside my Mounjaro KwikPen injections?
Yes, injectable Mounjaro does not directly interact with oral supplements. However, Mounjaro affects how your stomach processes food and absorbs nutrients, so timing and choice of supplements matter. Always discuss your supplement routine with your prescriber or pharmacist to ensure no interactions with other medications you're taking.
What's the difference between Mounjaro and Wegovy supplement needs?
Both medications slow gastric emptying, so nutritional considerations are similar. Mounjaro uses a dual GIP and GLP-1 mechanism, whilst Wegovy uses GLP-1 alone, but both may affect B12, iron, and calcium absorption. Individual needs depend on your weight loss rate, diet, and existing health conditions — your GP can assess what's right for you.
Should I take supplements if I'm not having side effects on Mounjaro?
Even without noticeable side effects, reduced food intake on Mounjaro may affect nutrient levels over time. A blood test from your GP can identify deficiencies. Preventative supplementation of B12, vitamin D, and iron is often recommended as a precaution during weight loss treatment, rather than waiting for symptoms to appear.
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.