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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Weight Loss on Methotrexate — What You Need to Know
Methotrexate is a commonly prescribed medication for conditions like rheumatoid arthritis and certain cancers. Many people taking methotrexate wonder whether they can lose weight safely while on this treatment. The answer is yes — weight loss is possible, though methotrexate can affect your appetite and metabolism in different ways. This guide explains what to expect and how to approach weight management UK while taking this medication, including when to involve your GP.
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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.
How Methotrexate Affects Weight and Appetite
Methotrexate affects weight through several mechanisms. Some people experience reduced appetite as a direct side effect — methotrexate can cause nausea, mouth ulcers, or taste changes that naturally lower food intake. Others find their appetite increases, or they experience fatigue that reduces physical activity, making weight gain more likely.
Additionally, methotrexate may slow metabolism slightly in some patients, though this effect is usually modest. The medication's impact on weight is highly individual — your underlying condition, overall health, and other medications you take all play a role.
- Appetite suppression is common in the first few weeks of methotrexate treatment
- Nausea typically improves over time as your body adjusts
- Weight changes are often related to reduced activity rather than the drug itself
- Folate supplementation (prescribed alongside methotrexate) helps minimise side effects including appetite issues
If you're struggling with significant appetite loss or weight changes, discuss this with your GP or rheumatologist — they may adjust your dose or timing.
Clinically BackedWeight Loss
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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.
Safe Weight Loss While Taking Methotrexate
Safe weight management while on methotrexate follows the same NHS principles as for anyone else: a modest calorie deficit combined with physical activity. The NHS recommends losing no more than 0.5 to 1 kg per week for sustainable results.
Key considerations: avoid very low-calorie diets (under 1200 kcal daily) without medical supervision, as methotrexate can affect nutrient absorption. Stay well-hydrated, eat protein-rich foods to preserve muscle, and ensure you're getting adequate folate and other micronutrients your GP has advised.
Use our free BMI calculator to track whether your weight is in a healthy range for your height. If you're interested in prescription weight loss medication options, discuss eligibility with your GP — some weight management medications may interact with methotrexate, so clinical assessment is essential.
- 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 weight loss injections while on methotrexate?
Possibly, but only with GP approval. Some GLP-1 weight loss injections (like Wegovy or Mounjaro) may interact with methotrexate or affect how it's absorbed. Your prescriber will assess whether it's safe for you individually. Never start any new medication without informing your GP that you're on methotrexate.
Will methotrexate prevent me from losing weight?
No, methotrexate does not prevent weight loss. However, its side effects — nausea, fatigue, appetite changes — can make weight management more challenging. Most people can lose weight successfully by combining a calorie deficit with physical activity, adjusted for how methotrexate affects them personally.
How much weight is safe to lose while taking methotrexate?
Aim for the NHS standard of 0.5 to 1 kg per week. Faster weight loss may increase muscle loss and stress on your body while managing a chronic condition. Avoid crash diets or very restrictive eating — your body needs adequate nutrients to tolerate methotrexate well.
Does methotrexate affect my BMI calculations?
No, BMI (body mass index) calculation is the same whether you're on methotrexate or not. Use our free BMI calculator to check your current BMI and healthy weight range for your height. BMI does not account for muscle mass, so discuss your results with your GP for personalised advice.
Should I tell my GP I want to lose weight while on methotrexate?
Yes, absolutely. Your GP or rheumatologist should know about any weight loss plans. They can advise on safe approaches for your specific condition, check that weight loss won't interfere with your treatment, and monitor your health during any dietary changes. This is especially important if you're considering prescription weight loss options.
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.