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 Low Mood — How It Compares to Wegovy
Both Mounjaro and Wegovy are prescription-only weight management injections that may affect mood in some people. Low mood is not commonly reported as a primary side effect in clinical trials, but some users report mood changes during treatment. This guide compares how the two medications have performed in trials, explains the mechanisms involved, and helps you understand what to expect. If you're considering either medication, your prescriber will assess your individual risk factors during clinical assessment.
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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.
Clinical Trial Data and Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways simultaneously. In the SURMOUNT-1 trial, low mood was reported in less than 1% of participants across all doses (2.5 mg to 15 mg). The trial focused primarily on weight loss outcomes rather than detailed mood monitoring.
Wegovy (semaglutide) is a GLP-1-only agonist. In the STEP-1 trial, depression was reported in approximately 2–3% of participants on the 2.4 mg maintenance dose. Again, mood was not the primary focus of the trial, meaning side effects may be under-reported compared to dedicated mental health monitoring.
The dual mechanism of Mounjaro theoretically could affect mood differently than Wegovy's single pathway, but head-to-head trial data specifically comparing mood outcomes does not exist. Both medications slow gastric emptying and affect appetite regulation through the same general pathways — any mood impact is likely related to gradual weight management, metabolic changes, or individual sensitivity rather than the medication mechanism itself.
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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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Individual Suitability and Prescriber Assessment
Neither medication is expected to cause low mood as a primary or common effect. However, individual responses vary significantly. Factors that influence mood during weight loss include: existing depression or anxiety (which may worsen with rapid change), medication interactions, nutritional deficiencies from gradual weight management, stress, and underlying metabolic factors.
Your prescriber will ask about your mental health history before prescribing either medication. If you have a history of depression, anxiety, or mood disorders, it is essential to disclose this during clinical assessment. Some people find that weight loss itself improves mood due to increased energy and confidence. Others may experience temporary mood dips during the adjustment period. Both medications are monitored — if low mood develops, your prescriber can adjust your dose, pause treatment, or switch medications.
Use our free GLP-1 weight loss calculator to explore projected outcomes with either medication, and discuss any mood concerns with your prescriber before starting 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 Mounjaro cause depression or low mood?
Low mood is not a commonly reported side effect of Mounjaro. In the SURMOUNT-1 clinical trial, it was reported in less than 1% of users. However, individual responses vary. Some people experience mood changes during gradual weight management or medication adjustment. Always inform your prescriber if you have a history of depression before starting treatment.
Is Wegovy more likely to cause low mood than Mounjaro?
Wegovy reported depression in approximately 2–3% of trial participants, slightly higher than Mounjaro. However, this difference may reflect differences in how trials monitored mood rather than true medication differences. No head-to-head trial comparing mood outcomes exists. Individual experience varies, and your prescriber can adjust treatment if mood changes occur.
What should I do if I experience low mood while taking Mounjaro or Wegovy?
Contact your prescriber immediately. Low mood during treatment may relate to gradual weight management, nutritional changes, or individual medication sensitivity. Your prescriber can adjust your dose, pause treatment, or explore alternatives. Do not stop the medication suddenly — always consult your healthcare provider first.
Does GLP-1 medication cause mood changes because of how it works?
GLP-1 and GIP work on appetite and blood sugar regulation, not directly on mood pathways in the brain. Mood changes during treatment are more likely linked to gradual weight management, metabolic adjustments, medication interactions, or underlying anxiety. This is why mental health history matters during clinical assessment.
How can I check my eligibility for Mounjaro or Wegovy in the UK?
Both medications require a UK prescription following clinical assessment. You'll need a BMI of 30 or above, or 27 with weight-related health conditions. Use our free BMI calculator to check your current status, then discuss options with your GP or a registered online prescriber who can evaluate your full medical history and suitability.
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