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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Does Mounjaro Cause Mood Swings?
Mood swings are not listed as a common or very common side effect of Mounjaro (tirzepatide) in UK clinical data, though some people report changes in mood or emotional wellbeing. Most mood-related changes reported are indirect — linked to appetite suppression, gradual weight management, or adjusting to medication rather than tirzepatide itself. If you're considering Mounjaro or currently taking it, understanding what to expect and when to seek support from your GP is essential. Our GLP-1 weight loss calculator can help you explore projected outcomes alongside realistic expectations for your health journey.
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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.
What Does Clinical Data Show About Mounjaro and Mood?
Clinical trials for Mounjaro (tirzepatide) — including the SURMOUNT-1 trial that supported UK licensing — did not identify mood swings as a primary side effect. The most commonly reported side effects were gastrointestinal: nausea, diarrhoea, vomiting, and constipation. However, indirect mood changes can occur for several reasons:
- Rapid appetite reduction: Some people experience changes in eating behaviour or food enjoyment, which can affect mood temporarily
- gradual weight management: Quick changes in body weight, even positive ones, can trigger emotional adjustment periods
- Blood sugar stabilisation: For people with type 2 diabetes or prediabetes, improved blood sugar control via tirzepatide may stabilise energy and mood
- Gastrointestinal side effects: Persistent nausea or diarrhoea can affect mood and wellbeing indirectly
- Dose titration effects: During Mounjaro dose escalation from 2.5mg up to 15mg, some people report temporary emotional adjustment
Depression or anxiety are not listed as expected side effects in the UK Mounjaro KwikPen information. If you experience significant mood changes, this is worth discussing with your GP.
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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.
When to Contact Your GP About Mood Changes
Contact your GP if you experience persistent low mood, anxiety, emotional numbness, or thoughts of self-harm after starting Mounjaro. These are not typical Mounjaro side effects and may indicate another health issue unrelated to the injection. Your GP can assess whether your mood changes are linked to the medication, the weight loss process itself, or something else entirely.
Mood is complex and individual — factors like stress, sleep quality, physical activity, diet quality, and social support all influence emotional wellbeing alongside any medication. Keep a brief mood log if helpful, noting when changes occur in relation to your Mounjaro doses and other life factors. This information helps your GP provide personalised support. Comparison with our BMI calculator can also contextualise your health progress and may ease adjustment to weight changes.
- 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?
Depression is not listed as a common side effect of Mounjaro in clinical trials or UK prescribing data. However, gradual weight management, appetite changes, or gastrointestinal side effects can indirectly affect mood. If you experience persistent low mood, contact your GP for assessment. Other factors like sleep, stress, and physical activity also influence mood.
How does Mounjaro compare to Wegovy for mood effects?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are GLP-1 or dual GIP/GLP-1 agonists with similar side effect profiles. Mood changes are not listed as common for either. Mounjaro vs Wegovy differences relate mainly to mechanism and weight loss magnitude, not emotional effects. Clinical trial data shows similar mood safety for both.
Is mood change a reason to stop Mounjaro?
Mood changes alone are not a standard reason to stop Mounjaro. However, if you experience severe or persistent mood symptoms, discuss this with your GP immediately. They can assess whether the mood change is medication-related and explore alternatives. Never stop Mounjaro without medical guidance.
Does Mounjaro affect serotonin or brain chemistry?
Mounjaro (tirzepatide) works primarily in the gut and pancreas, activating GIP and GLP-1 receptors. It does not directly target brain serotonin systems like antidepressants do. Mood effects from Mounjaro are indirect — through appetite, weight, and blood sugar changes — not direct neurochemical effects.
What if my mood improves on Mounjaro?
Many people report improved mood and confidence linked to weight loss success and increased energy from better blood sugar control. This is a positive outcome. Monitor your overall wellbeing, track progress with our free progress tracker, and discuss any changes with your GP to ensure your mental and physical health are both supported.
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.