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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Ulcerative Colitis and Weight Loss — UK Medication Options
Managing weight while living with ulcerative colitis presents unique challenges, as the condition often affects appetite, nutrient absorption, and energy levels. If you're looking to lose weight safely, UK-licensed prescription medications are available for eligible adults. This guide explores prescription weight management options in the UK, how they work alongside ulcerative colitis treatment, and how to discuss them with your GP. Always consult your healthcare team before starting any new weight loss treatment, as some medications may interact with your current colitis management plan.
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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.
UK Prescription Weight Loss Medications for Ulcerative Colitis
Three prescription-only medications are currently licensed in the UK for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These GLP-1 and GIP receptor agonist medications work by reducing appetite and supporting feeling fuller after smaller meals. They may help with weight loss uk goals, though individual results vary significantly.
If you have ulcerative colitis and a BMI of 30 or above, or 27–29.9 with weight-related health conditions, you may be eligible. However, these medications can affect how your digestive system works—slowing stomach emptying and altering gut motility—which is particularly relevant for inflammatory bowel conditions. Clinical trials showed that participants on Mounjaro lost an average of 15–21% of body weight, and those on Wegovy lost approximately 15%, but this depends entirely on your individual circumstances and medical history.
Your GP or prescriber must assess whether these are safe for your specific colitis management and current medications before prescribing.
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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.
NHS vs Private Weight Loss Medication — Finding Your Option
Access to prescription weight loss medication in the UK comes through two routes. NHS access is via specialist tier 3 weight management services, typically following a GP referral. However, availability varies significantly by region and waiting lists can be lengthy. Private access is available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber—no NHS referral needed.
Before pursuing either route, discuss your ulcerative colitis diagnosis with your GP or prescriber. They'll assess whether glp-1 weight loss medication is safe alongside your current treatment (such as aminosalicylates, corticosteroids, or biologics). You can calculate your BMI and track your weight loss journey using free tools to monitor progress alongside any prescription weight management plan. Your GP can also advise on whether NHS or private options suit your situation best.
- 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 Mounjaro or Wegovy if I have ulcerative colitis?
Possibly, but only following clinical assessment. GLP-1 medications affect gut motility and digestive function, which matters when managing inflammatory bowel disease. Your GP or gastroenterologist must approve it and review potential interactions with your current colitis medications (such as biologics or immunosuppressants) before you start.
Will weight loss medication affect my ulcerative colitis?
GLP-1 medications can affect digestion and may alter symptoms. Some people experience changes in bowel patterns. This is why prescriber assessment is essential—they'll weigh the benefits of weight management against potential impacts on your colitis control. Report any changes in symptoms immediately.
How do I get prescription weight loss medication on the NHS if I have ulcerative colitis?
Ask your GP for a referral to your local tier 3 specialist weight management service. They'll assess your eligibility (BMI 30+, or 27+ with weight-related conditions) and whether it's safe given your ulcerative colitis. NHS availability and waiting times vary by region.
What's the difference between NHS and private prescription weight loss options?
NHS medication is accessed through specialist referral services but availability is patchy and waiting lists are long. Private prescriptions are available faster through online assessments but cost approximately £129–£320 monthly depending on dose. Both require a legitimate clinical assessment and prescription from a UK-licensed prescriber.
Can I use a BMI calculator to check if I'm eligible for weight loss medication?
Yes—calculate your BMI using our free BMI calculator above to see where you fall. Eligibility typically starts at BMI 30, or 27 with weight-related conditions. However, your prescriber will assess overall health, colitis status, and medications before confirming suitability.
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.