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 Make You Angry? What the Evidence Shows
Mood changes and irritability are not listed as common side effects of Mounjaro in the UK clinical trial data, though some people using this tirzepatide injection report feeling emotionally different during treatment. The majority of reported side effects relate to digestion — nausea, diarrhoea, and constipation — rather than mood. This guide explains what the evidence shows, who might be affected, and how to access Mounjaro or discuss alternatives with your GP if you have concerns about emotional side effects.
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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.
What Does the Clinical Evidence Show About Mounjaro and Mood?
Mounjaro (tirzepatide) is a prescription-only GIP and GLP-1 receptor agonist approved in the UK for weight management in adults. In the SURMOUNT clinical trials that led to UK licensing, mood changes and anger were not reported as common side effects. The most frequently reported adverse effects were gastrointestinal — nausea affected more than 1 in 10 participants, followed by diarrhoea, vomiting, and constipation.
However, any medication can affect individuals differently. Some people using Mounjaro have reported feeling irritable, anxious, or experiencing emotional shifts, though these reports are not formally classified as frequent side effects. Weight loss medications can indirectly affect mood through rapid weight changes, dietary shifts, or underlying metabolic adjustments. Additionally, improved energy levels and reduced appetite may feel psychologically unusual initially.
If you experience mood changes while using Mounjaro, this should be discussed with your prescriber. They can assess whether the injection is the cause, explore dose adjustments, or discuss alternative weight management options. Your GP can also help rule out other medical causes of mood changes.
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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.
Accessing Mounjaro in the UK — Cost and Routes
NHS access to Mounjaro requires referral to a tier 3 specialist weight management service, which varies significantly by region. Waiting lists can be lengthy in many areas. NICE has approved tirzepatide (Mounjaro) for use within NHS specialist services for eligible adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions.
Private prescription route: Mounjaro is available through GPhC-registered online pharmacies following an online consultation with a UK-licensed prescriber. Costs typically range from £150–£300 per month depending on dose, with higher doses (10–15mg) at the upper end. An online consultation assesses your eligibility, medical history, and suitability before a prescription is issued. This route bypasses NHS waiting lists and is accessible without a GP referral, though a full medical assessment is still required.
- 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 anger or mood swings?
Anger and mood swings are not listed as common side effects in UK clinical trials. However, individual experiences vary. gradual weight management, dietary changes, and metabolic shifts can indirectly affect mood. If you experience mood changes while using Mounjaro, discuss this with your prescriber or GP to explore whether the injection is responsible or if another cause should be investigated.
What are the most common Mounjaro side effects in the UK?
The most frequently reported side effects are gastrointestinal: nausea (affecting more than 1 in 10 people), diarrhoea, vomiting, and constipation. Other common effects include stomach pain, indigestion, and injection site reactions. These typically decrease over time as your body adjusts to the dose.
How do I access Mounjaro in the UK if I'm concerned about side effects?
You can discuss Mounjaro through your GP, who may refer you to an NHS specialist weight management service, or pursue private prescription through an online clinical assessment with a UK-licensed prescriber. Either route allows you to discuss side effect concerns before starting and to switch or stop if needed.
Does Mounjaro dose titration affect mood?
Mounjaro uses gradual dose titration — starting at 2.5mg and increasing weekly to the maintenance dose. This stepped approach may help your body adjust and reduce side effects. Emotional side effects are uncommon at any dose stage, but if they occur, your prescriber can adjust your treatment plan.
What should I do if Mounjaro is making me feel angry?
Contact your prescriber or GP immediately. They can assess whether Mounjaro is responsible, explore dose adjustments, or discuss alternatives like Wegovy or lifestyle-based weight management. Your mental health is as important as physical health outcomes, and treatment should be stopped if it's affecting your wellbeing.
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.