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 Medicine Should You Not Take With Wegovy?
If you're prescribed Wegovy (semaglutide), knowing which medicines to avoid is essential for your safety. Wegovy can interact with certain medications, potentially reducing their effectiveness or increasing side effects. This guide explains the key drug interactions, what your GP needs to know, and how to use Wegovy safely alongside other treatments. Always discuss your complete medication list with your prescriber before starting this GLP-1 receptor agonist.
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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.
Key Medicines That May Interact With Wegovy
Oral contraceptives (birth control pills) are the most significant interaction. Wegovy may slow the absorption of oral medications in your stomach, meaning your contraceptive may not work as effectively. The UK prescribing guidance recommends using a barrier method (condoms) or switching to a non-oral contraceptive for at least 4 weeks after starting Wegovy and for 4 weeks after each dose increase. This timing is critical because gastrointestinal effects typically improve as your body adjusts.
- Diabetes medications: If you take insulin or sulphonylurea drugs (like gliclazide), your doses may need adjustment as Wegovy improves blood sugar control. Your GP must monitor you closely to avoid hypoglycaemia (low blood sugar).
- Certain oral medications: Any medicine taken by mouth may have reduced absorption due to slower stomach emptying, including some antibiotics and regular painkillers.
- Blood pressure medications: Weight loss itself lowers blood pressure, so your prescriber may need to review your antihypertensive doses.
Your prescriber should assess all your current medicines before issuing a Wegovy prescription. Be transparent about every medication, supplement, and herbal remedy you take.
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.
What You Must Tell Your GP or Prescriber
Before starting Wegovy (semaglutide), provide a complete list of everything you're taking—prescribed medicines, over-the-counter products, vitamins, and supplements. Specific medications that warrant particular caution include thyroid hormones (Wegovy may affect absorption), certain heart medications, and any drugs for chronic kidney disease. Your prescriber will assess whether Wegovy is safe for you or whether dose adjustments to your other medicines are needed. Never stop or change any medication without consulting your GP or prescriber. If you experience unusual symptoms after starting Wegovy—such as innovative bleeding on contraception, unexpected changes in blood sugar, or reduced effectiveness of your regular medicines—contact your healthcare provider immediately.
- 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 paracetamol or ibuprofen with Wegovy?
Paracetamol and ibuprofen can generally be taken with Wegovy, but Wegovy may slow their absorption slightly. Take them with water and avoid long-term ibuprofen use without GP guidance, as this increases digestive side effect risk when combined with Wegovy.
Is Wegovy safe with blood pressure medication?
Yes, but your blood pressure should be monitored regularly. Wegovy-induced weight loss can lower blood pressure further, so your prescriber may need to reduce your antihypertensive doses. Never adjust doses yourself—always consult your GP.
What if I'm on the contraceptive pill and starting Wegovy?
Switch to a barrier method or alternative contraception for 4 weeks after starting Wegovy and after each dose increase. Oral contraceptives may not work reliably because Wegovy slows stomach emptying and medication absorption.
Can I take Wegovy with thyroid medication?
Wegovy may affect thyroid medication absorption. Your GP should monitor your thyroid function regularly if you take levothyroxine or other thyroid treatments. Take thyroid medication at least 30 minutes before eating or taking Wegovy injections.
What if I take insulin—can I use Wegovy?
Yes, but insulin doses typically need adjustment because Wegovy improves blood sugar control. Your GP must monitor you closely to prevent hypoglycaemia. Never adjust insulin yourself; always follow your prescriber's guidance.
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.