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
Which Antidepressants Cause Weight Loss?
Some antidepressants may help with weight loss as a secondary effect, though most are prescribed primarily for mental health rather than weight management. If you're struggling with weight and taking antidepressants, your GP can discuss whether your current medication is right for you and explore alternatives if needed. Understanding how different antidepressants affect weight is important for making informed healthcare decisions. This guide explains which medications may support weight loss, how they work, and what to expect when weight management becomes part of your health plan in the UK.
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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.
Antidepressants Associated with Weight Loss
Several antidepressants have been linked to weight loss or neutral weight effects, though results vary significantly between individuals:
- Fluoxetine (Prozac) — often associated with initial weight loss, though this may plateau after several months. Some people regain weight over time.
- Topiramate — an anticonvulsant sometimes used off-label with antidepressants, commonly associated with weight loss.
- Bupropion (Wellbutrin) — frequently linked to weight loss or weight neutrality. May suppress appetite compared to other antidepressants.
- Sertraline (Lustral) — generally weight-neutral or associated with modest weight loss in some patients.
- Paroxetine (Seroxat) — more likely to cause weight gain, but weight loss is possible in some individuals.
Importantly, weight changes with antidepressants are highly individual. Your response depends on your metabolism, dosage, duration of treatment, diet, and physical activity. Always discuss any concerns about weight with your GP rather than stopping medication without guidance.
Clinically BackedWeight Loss
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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.
Weight Loss Medication vs. Antidepressants
If you're overweight and struggling with depression or anxiety, your GP may discuss different approaches. Antidepressants treat mental health conditions; they're not primarily designed for weight management. For dedicated weight management in the UK, prescription options like GLP-1 injections (Wegovy or Mounjaro) are specifically licensed and may be more effective for weight loss alongside lifestyle changes.
However, these are separate treatments. If you take antidepressants and want to explore prescription weight loss medication, your GP or a specialist can assess whether it's safe to use both together. Some medications interact, so professional guidance is essential. Use our free GLP-1 weight loss calculator to estimate potential outcomes if weight management medication is appropriate for you.
- 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 I stop my antidepressant to lose weight?
No — stopping antidepressants without medical guidance is unsafe and can cause serious withdrawal effects and relapse of depression or anxiety. If you're concerned about weight gain, speak to your GP. They may adjust your dose, switch you to a different antidepressant, or discuss additional weight management strategies alongside your current medication.
Will antidepressants prevent weight loss?
Most antidepressants don't prevent weight loss, but some (like paroxetine) are more likely to cause weight gain. Others (like fluoxetine or bupropion) may be weight-neutral or associated with modest loss. Individual responses vary. Your GP can discuss which antidepressant might work best for both your mental health and weight management goals.
What's the difference between antidepressants and weight loss injections?
Antidepressants treat depression and anxiety; weight loss injections (GLP-1 medications like Wegovy) are licensed specifically for weight management. They work differently and address different health issues. You may take both if appropriate, but this requires medical assessment to check for interactions. Your GP or specialist can advise.
How long does it take to see weight changes on antidepressants?
Weight changes can take several weeks to months to become noticeable. Initial weight loss with some antidepressants may plateau after a few months. Since antidepressants primarily treat mental health, weight changes are usually a secondary effect rather than the main goal of treatment.
Should I ask my GP about weight loss medication as well?
Yes. If you're overweight and interested in prescription weight loss options, discuss this with your GP. They'll assess your BMI, overall health, and whether weight management medication is suitable for you. Check your BMI using our free calculator to prepare for this conversation with your healthcare team.
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.