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
Antidepressants That Cause Weight Loss — UK Perspective
Some antidepressants can indeed cause weight loss as a side effect, though this is less common than weight gain. Bupropion (Wellbutrin) and fluoxetine (Prozac) are two examples used in the UK that may support modest weight reduction in some people. However, if you're specifically seeking weight management options, the NHS and private healthcare now offer prescription medications designed for this purpose, which may be more effective and better supported by clinical evidence. This guide explains the antidepressant angle and explores dedicated weight management options available to you.
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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.
UK-Licensed Prescription Weight Management Options
If weight loss is your primary goal, rather than treating depression, the UK now has prescription weight management medications specifically approved and designed for this purpose. These are more effective than antidepressants for weight loss and are supported by strong clinical evidence.
Three main options are available:
- Mounjaro (tirzepatide) — A once-weekly injection. In clinical trials, it helped adults lose an average of 15–21% of body weight alongside diet and exercise changes.
- Wegovy (semaglutide) — A once-weekly GLP-1 injection. Clinical trials showed average weight loss of around 15% of body weight.
- Saxenda (liraglutide) — A daily injection option, though less commonly prescribed than the weekly options.
All three are prescription-only medicines requiring a clinical assessment from a GP or licensed prescriber to determine eligibility. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and check your BMI instantly with our BMI calculator to see where you stand on NHS guidelines.
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.
How to Access Prescription Weight Loss in the UK
You can access prescription weight loss medication through two routes:
- NHS route: Speak to your GP about referral to a specialist weight management service. Availability and waiting times vary by region, but the NHS now funds tirzepatide (Mounjaro) through specialist services for eligible adults.
- Private route: Online consultations with UK-licensed prescribers, typically faster and without NHS waiting lists. A clinical assessment determines if treatment is suitable for you based on your BMI and health.
Eligibility generally requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or high blood pressure. Track your weight loss progress using our free progress tracker once you start any weight management plan.
- 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.
Do antidepressants cause weight loss?
Some antidepressants can cause modest weight loss, particularly bupropion (Wellbutrin) and fluoxetine (Prozac). However, weight loss is not assured and is less common than weight gain with antidepressants. Individual responses vary significantly, and they are not designed or approved specifically for weight management.
Which antidepressants might support weight loss?
Bupropion and fluoxetine are the most commonly cited antidepressants associated with weight loss in the UK. Other SSRIs occasionally show weight-neutral or modest weight-reducing effects. Your GP can advise on which might be suitable for your specific situation if you need antidepressant treatment.
What's the difference between antidepressants and weight loss medications?
Antidepressants treat depression; weight loss is an incidental side effect. Prescription weight loss medications like Mounjaro and Wegovy are specifically designed and approved for weight management, with strong clinical evidence for weight loss results of 15–21% of body weight.
Can I use antidepressants specifically for weight loss?
No — antidepressants should only be prescribed for depression or anxiety disorders. Using them solely for weight loss would be off-label and not recommended. If weight loss is your goal, prescription weight management medications are a more appropriate, evidence-based option available in the UK.
How do I know if I'm eligible for NHS weight loss medication?
Eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Speak to your GP about referral to your local specialist weight management service, or use our free BMI calculator to check where you stand against NHS guidelines first.
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.