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 Mental Health Side Effects — What You Need to Know
Mental health side effects are an important consideration when discussing Mounjaro (tirzepatide) or Wegovy (semaglutide) weight loss treatment in the UK. While gastrointestinal side effects like nausea and diarrhoea are most commonly reported, some users and healthcare professionals have raised concerns about potential mood changes, anxiety, and depression during treatment. This guide compares the evidence for mental health effects between Mounjaro and Wegovy, explains what clinical trials showed, and helps you understand what to discuss with your GP or prescriber before starting either medication.
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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.
Mounjaro vs Wegovy — Mental Health Side Effects Comparison
Mounjaro (tirzepatide) and Wegovy (semaglutide) work through similar but distinct mechanisms: Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. This difference may theoretically affect side effect profiles, though direct clinical trial comparisons specifically for mental health are limited.
In the SURMOUNT clinical trials (Mounjaro), depression and anxiety were not reported as common side effects. However, post-launch reports and real-world data suggest some users experience mood changes, which may relate to gradual weight management, medication interactions, or individual neurochemistry.
For Wegovy, the STEP clinical trials similarly showed depression and anxiety at rates comparable to placebo. However, anecdotal reports from users and healthcare providers in the UK have noted similar concerns about mood fluctuations during treatment.
- Both medications may cause fatigue and dizziness, which can indirectly affect mood
- gradual weight management itself can sometimes trigger emotional adjustment periods
- Neither medication is known to cause clinically significant depression at typical doses
- Mental health monitoring by a GP is recommended during treatment
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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.
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Which Medication Is Right for Your Mental Health?
There is no clear evidence that either Mounjaro or Wegovy is superior for mental health outcomes. Individual responses vary significantly based on genetics, existing mental health conditions, concurrent medications, and personal circumstances.
If you have a history of depression, anxiety, or other mental health conditions, inform your prescriber before starting either medication. A clinical assessment will determine suitability and establish a monitoring plan. Your GP can discuss:
- Whether GLP-1 medication is appropriate for your mental health profile
- How to monitor your mood during the first 4–8 weeks of treatment
- Potential interactions with antidepressants or anti-anxiety medications
- When to seek support if mood changes occur
Both medications require prescription and ongoing GP or prescriber oversight in the UK. Track mood changes using our free progress tracker alongside your weight loss journey.
- 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 Mounjaro cause depression or anxiety?
Clinical trials did not show depression or anxiety as common side effects of Mounjaro. However, some users report mood changes during treatment. These may relate to gradual weight management, medication interactions, or individual factors. Always inform your prescriber of any mood changes, and speak to your GP if you have concerns.
Is Wegovy safer for mental health than Mounjaro?
There is no clinical evidence that Wegovy is safer than Mounjaro for mental health, or vice versa. Both are GLP-1 receptor agonist medications with similar safety profiles in clinical trials. Individual responses vary. A prescriber can help you choose based on your personal health profile.
What should I monitor for mood-wise when taking Mounjaro or Wegovy?
Monitor for persistent low mood, loss of interest in activities, increased anxiety, or significant changes in sleep or appetite. These are worth discussing with your GP, even if they seem mild. Most users experience no mental health changes, but early reporting helps your healthcare team support you.
Can GLP-1 medications interact with antidepressants?
Mounjaro and Wegovy may affect how quickly your stomach empties, which could theoretically reduce absorption of some oral medications including some antidepressants. Always inform your prescriber of all medications you take. They may recommend timing doses separately or monitoring effectiveness.
How long after starting Mounjaro or Wegovy should I assess mental health effects?
Most side effects appear within the first 2–4 weeks. Mental health effects, if they occur, typically emerge during the first 8 weeks of treatment. Your prescriber should schedule check-ins at 2, 4, and 8 weeks to assess how you're managing. Report any concerns promptly to your GP.
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