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
Weight Loss and Antidepressants — What You Need to Know
Some antidepressants can affect weight, making weight loss more challenging for people taking them. The relationship between mental health medication and weight is complex — certain antidepressants may increase appetite or slow metabolism, whilst others have less impact on weight. If you're taking an antidepressant and concerned about weight management, your GP can help you explore options. These might include adjusting your medication, lifestyle changes, or prescription weight loss medication used alongside your current treatment. Understanding how your specific antidepressant affects your body is the first step towards sustainable weight management.
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.
Which Antidepressants Are Most Likely to Affect Weight?
Different antidepressants have varying effects on weight and appetite. Tricyclic antidepressants (such as amitriptyline) and some SSRIs (like paroxetine) are more commonly associated with weight gain, whilst others like sertraline or citalopram may have neutral or modest effects. Mirtazapine, often used for depression with sleep problems, frequently increases appetite and can lead to weight gain. The reasons vary: some antidepressants may increase hunger signals, slow metabolism slightly, or affect how your body stores fat.
- Weight changes typically occur within the first few weeks of starting medication
- Gaining 2–5 kg in the first months is relatively common with some antidepressants
- Individual responses vary significantly — some people experience no weight change at all
- Your GP can discuss which antidepressants have the lowest weight-related side effects for your situation
Never stop or change your antidepressant without medical guidance, even if you're concerned about weight. Your mental health is the priority — but there are solutions available.
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.
Managing Weight Whilst Taking Antidepressants
Sustainable weight management alongside antidepressants requires a multi-faceted approach. Lifestyle changes — increased physical activity, balanced nutrition, and reduced-calorie intake — remain foundational. Many people find that even modest changes (like walking daily and reducing sugary drinks) help counter weight-related side effects. If lifestyle changes alone aren't enough, speak with your GP about other options. These include switching to a different antidepressant with a lower weight impact, or discussing prescription weight loss medication such as GLP-1 injections. Recent weight loss injections like Wegovy or Mounjaro may be considered alongside your antidepressant with proper medical supervision. Our free GLP-1 weight loss calculator can help you explore potential weight loss projections if your GP recommends this route. Track progress using our free progress tracker to see what's working 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 take weight loss injections if I'm on antidepressants?
Yes, but only under GP supervision. Weight loss injections like Wegovy (semaglutide) and Mounjaro (tirzepatide) can be used alongside most antidepressants. However, your prescriber must review all your medications to check for interactions. Some antidepressants (like tricyclics) may require closer monitoring. Always inform any prescriber about all medications you're taking, including antidepressants, before starting weight loss treatment.
Will changing my antidepressant help me lose weight?
Switching to an antidepressant with lower weight-related side effects may help, but it's not assured. Your GP must balance weight concerns against your mental health needs — the right antidepressant for your depression is the priority. Some alternatives include sertraline, citalopram, or fluoxetine, which tend to have more neutral weight effects. Never change antidepressants without medical guidance.
How long does it take to see weight changes after starting an antidepressant?
Weight changes typically appear within the first 4–8 weeks of starting an antidepressant, though this varies. Some people gain weight quickly, whilst others experience gradual changes over months. If weight gain becomes a significant concern, discuss it with your GP at your follow-up appointment — usually around 2–4 weeks after starting.
What's the safest way to lose weight on antidepressants?
A combination approach works best: maintain a balanced, reduced-calorie diet, increase physical activity gradually, manage stress, and ensure adequate sleep. These lifestyle factors support both mental health and weight loss. If lifestyle changes aren't sufficient after 3–6 months, discuss prescription options with your GP. Our BMI calculator and weight converter can help you track progress in measurements that make sense to you.
Do all SSRIs cause weight gain?
No — weight effects vary among SSRIs. Sertraline and citalopram tend to be weight-neutral or cause minimal gain, whilst paroxetine is more likely to increase weight. Fluoxetine can even support modest weight loss in some people. Your GP can prescribe an SSRI based on both your depression symptoms and weight considerations. If weight gain occurs, alternatives may be available.
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.