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 Eat Peanut Butter On Mounjaro?
Yes, you can generally eat peanut butter while taking Mounjaro (tirzepatide), but portion control is important. Mounjaro is a prescription-only GLP-1 and GIP receptor agonist that reduces appetite and slows digestion, which means you'll naturally eat less and feel fuller faster. However, peanut butter is calorie-dense and can be difficult to digest for some people taking Mounjaro, particularly in the first few weeks when gastrointestinal side effects are most common. This guide explains what to eat, what to avoid, and how to manage your diet while on Mounjaro treatment in the UK.
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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.
Foods to Avoid or Limit While Taking Mounjaro
When you start Mounjaro or increase your dose, your digestive system needs time to adjust. High-fat, high-sugar, and calorie-dense foods like peanut butter can trigger nausea, diarrhoea, vomiting, or stomach pain—the most common side effects reported in UK clinical trials. If you want to eat peanut butter, start with very small amounts (1–2 teaspoons) and monitor how your body responds.
- High-fat foods: Fried foods, fatty meats, full-fat dairy, and oil-based spreads—slowed digestion means these stay in your stomach longer, causing discomfort
- High-sugar foods: Cakes, biscuits, sweets, sugary drinks—can worsen nausea and contribute to rapid digestion issues
- Processed foods: Takeaways, processed snacks—often high in both fat and sugar, making them especially problematic
- Large meals: Mounjaro significantly reduces appetite; eat smaller portions more frequently instead
Most people on Mounjaro naturally avoid these foods because they feel unpleasant, but intentionally choosing lighter, protein-rich options helps you tolerate treatment better and lose weight more effectively.
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.
Getting Mounjaro in the UK — Cost and Access Routes
Mounjaro is available in the UK through two routes: NHS specialist weight management services and private online prescribing. NHS access typically requires referral from your GP to a tier 3 or tier 4 weight management service, though availability varies significantly by region (ICB) and waiting times can be months or longer. Private access is faster—online consultations with UK-licensed prescribers cost approximately £129–£320 monthly depending on your dose, plus ongoing prescription fees. Your prescriber will assess your eligibility based on BMI (30 or above, or 27+ with weight-related health conditions like type 2 diabetes or high blood pressure), medical history, and current medications before issuing a prescription to a GPhC-registered pharmacy.
- 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 eat peanut butter in the first two weeks of Mounjaro?
It's best to avoid peanut butter during your first two weeks, particularly if you experience nausea or stomach upset. Start with bland, protein-rich foods like chicken breast, white fish, eggs, or plain Greek yoghurt instead. Once your body adjusts and gastrointestinal side effects settle, small amounts of peanut butter may become tolerable.
What's the difference between Mounjaro and Wegovy for diet tolerability?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) slow digestion and reduce appetite similarly, so dietary tolerance is comparable. Mounjaro's dual GIP and GLP-1 mechanism may cause slightly different side effect patterns for some individuals, but no evidence suggests either is definitively better or worse for peanut butter tolerance specifically.
How much weight can I expect to lose on Mounjaro?
Clinical trials showed Mounjaro helped participants lose an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly. Use our GLP-1 weight loss calculator to estimate potential weight loss at different Mounjaro doses—results depend on dose, diet, exercise, and personal metabolism.
What happens if peanut butter triggers side effects on my Mounjaro dose?
If peanut butter causes nausea, diarrhoea, or stomach pain, simply avoid it for now. Most side effects improve as your body adapts to the dose (typically by week 4–6). Your GP or prescriber can advise if symptoms persist, but usually reducing high-fat foods resolves the issue quickly.
Can I use our BMI calculator to track my progress on Mounjaro?
Yes—calculate your current BMI using our free BMI calculator on this page, then track your weight loss over time using our progress tracker. Monitoring your BMI alongside weight helps you understand your health context beyond the number on the scale, especially when combined with regular GP check-ins on your Mounjaro dose titration plan.
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.