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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Mounjaro And Lamotrigine — What You Need To Know
If you're taking lamotrigine and considering Mounjaro (tirzepatide), it's important to understand how these medications interact. Mounjaro is a prescription-only weight management injection licensed in the UK, while lamotrigine is an anticonvulsant and mood stabiliser commonly prescribed for epilepsy and bipolar disorder. The good news is that there are no direct contraindications between these two medications, but your prescriber needs to assess your individual health situation before prescribing. Always inform any healthcare professional about all medications you're currently taking, including lamotrigine, before starting Mounjaro.
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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 Mounjaro And Lamotrigine Work Together
Mounjaro is a dual GIP and GLP-1 receptor agonist that works by regulating appetite and supporting weight management through natural hormone pathways. It does not interfere with lamotrigine's mechanism of action, which involves stabilising electrical activity in the brain and regulating sodium channels. However, because Mounjaro slows gastric emptying (how quickly food leaves your stomach), it may theoretically affect the absorption of some oral medications, including lamotrigine. The extent of this interaction is generally considered minimal, but it's something your prescriber should be aware of. Your GP or specialist will review your complete medication list and assess whether the benefits of Mounjaro outweigh any potential risks in your case. If both medications are suitable, they can typically be used together with appropriate monitoring and dose adjustments if needed.
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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 To Tell Your Prescriber Before Starting Mounjaro
Before beginning Mounjaro, provide your prescriber with a full list of all medications, supplements, and herbal products you're taking — including your lamotrigine dose and indication. Mention any previous issues with medication absorption, stomach problems, or seizure control. If you're taking lamotrigine for epilepsy management, your prescriber may want to liaise with your neurologist or epilepsy specialist to ensure Mounjaro won't affect seizure control. If you're on lamotrigine for bipolar disorder, inform your psychiatrist or mental health team about your plans to start Mounjaro. Your prescriber may recommend monitoring your lamotrigine levels through blood tests, or adjusting your lamotrigine dose if any changes in symptom control are noticed. Open communication with all your healthcare providers is essential for safe, effective treatment.
- 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 if I'm on lamotrigine?
There are no direct contraindications between Mounjaro and lamotrigine. However, because Mounjaro slows stomach emptying, it may slightly affect oral medication absorption. Your prescriber can assess whether both medications are suitable for you based on your individual health. Always disclose your lamotrigine use before starting Mounjaro.
Will Mounjaro affect my seizure control if I take lamotrigine for epilepsy?
Mounjaro is not expected to directly affect seizure control, but the potential for altered lamotrigine absorption means your neurologist should be informed. They may recommend blood tests to monitor lamotrigine levels or adjust your dose if needed. Report any changes in seizure patterns to your healthcare team immediately.
How do I access Mounjaro in the UK if I'm on lamotrigine?
Mounjaro is available through NHS specialist weight management services (with referral from your GP) or via private prescription following an online clinical assessment. Either route requires disclosure of your lamotrigine use. The prescriber will review whether it's safe for you to start.
Should my lamotrigine dose be changed if I start Mounjaro?
Your prescriber may recommend monitoring your lamotrigine blood levels after starting Mounjaro to ensure therapeutic levels remain stable. Dose adjustments are only made if monitoring shows a significant change. Never adjust your lamotrigine dose without medical guidance — maintaining seizure or mood control is essential.
What should I do if I experience changes in symptoms after starting Mounjaro?
Contact your prescriber or specialist immediately if you notice changes in seizure frequency, mood symptoms, appetite loss beyond expected, nausea, or any other concerning changes. Report all changes — your healthcare team may need to adjust either medication. Keep all scheduled appointments for monitoring and blood tests.
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.