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
Mounjaro Side Effects: Mental Health Considerations in the UK
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK, and like all medications, it can affect mental health and mood in some people. While most users tolerate it well, understanding potential mental health side effects is important when considering this treatment. This guide covers what the NHS and UK healthcare professionals recommend monitoring, supported by current evidence and clinical experience.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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.
Mental Health Side Effects and What the Evidence Shows
Mounjaro is a dual GIP and GLP-1 receptor agonist that works by affecting hunger and satiety signals in the brain. Because it influences these pathways, mental health effects are possible, though not common. The main mental health considerations reported include mood changes, anxiety, and in rare cases, depressive symptoms.
Common mental health-related effects reported in clinical practice include:
- Mood fluctuations or emotional changes
- Anxiety or nervousness
- Sleep disturbances affecting mood
- Changes in motivation or interest in activities
- Fatigue, which can affect mental wellbeing
It is important to note that clinical trial data for Mounjaro did not show a significant increase in depression or serious mental health events. However, individual experiences vary. If you have a history of depression, anxiety, or other mental health conditions, your prescriber must assess this before you start Mounjaro. Your GP or prescriber should discuss your mental health history during the clinical assessment.
Clinically BackedWeight Loss
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 Monitoring and When to Contact Your GP
The NHS recommends that anyone taking Mounjaro should monitor their mental health and mood regularly. If you notice persistent low mood, anxiety, loss of interest in activities you normally enjoy, or thoughts of self-harm, contact your GP immediately — do not wait for a routine appointment.
Keep an open conversation with your prescriber about how you are feeling emotionally. Some mood changes may be temporary as your body adjusts to the medication, while others may require dose adjustment or stopping the medication. Your GP can refer you to mental health support through NHS talking therapies (IAPT) or specialist services if needed. Remember that weight loss itself can also improve mood and mental health for many people, so the overall impact is individual.
- 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?
Clinical trials did not show a significant increase in depression rates with Mounjaro. However, mood changes and low mood are possible in some individuals. If you develop persistent depression symptoms, contact your GP immediately. Always mention any history of depression or mental health conditions to your prescriber before starting Mounjaro.
Is Mounjaro safe if I have anxiety?
Mounjaro can be prescribed to people with anxiety, but your prescriber needs to know about your anxiety history during the clinical assessment. Some people report anxiety as a side effect, while others find their anxiety improves with weight loss. Your GP can monitor your mental health and adjust treatment if needed.
What mental health monitoring should I do on Mounjaro?
Monitor your mood, sleep, motivation, and emotional wellbeing regularly. Keep a simple note of any changes. Report persistent low mood, anxiety, sleep problems, or loss of interest in activities to your GP. Early communication with your healthcare provider helps catch any issues quickly.
Can I take Mounjaro if I'm on antidepressants?
Yes, Mounjaro can be taken with antidepressants, but inform your prescriber of all medications you take. Some antidepressants may interact or affect how well Mounjaro works. Your GP or prescriber will assess compatibility and may monitor you more closely.
How long do mental health side effects last?
Most side effects settle within a few weeks as your body adjusts to the medication. However, if mental health changes persist beyond 4–6 weeks, contact your GP. They may adjust your dose or recommend stopping Mounjaro. Never stop suddenly without medical 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.