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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Weight Loss and Sertraline — What You Need to Know
Sertraline is an SSRI antidepressant commonly prescribed in the UK, and many people taking it wonder about its impact on weight management. Sertraline can sometimes cause weight gain as a side effect, which may make weight loss more challenging. However, if you're struggling with your weight and eligible for support, the UK offers several prescription weight management options alongside lifestyle changes. Understanding how sertraline affects your weight, and what licensed alternatives exist, helps you make informed decisions with your GP about your health.
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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.
UK-Licensed Weight Management Options
If you're overweight or obese and looking for prescription support beyond lifestyle changes, several licensed weight management medications are available in the UK. These are prescription-only options that work differently from sertraline:
- Mounjaro (tirzepatide) — a dual GIP and GLP-1 receptor agonist injected once weekly. Clinical trials showed participants lost an average of 15–21% of body weight alongside diet and exercise changes.
- Wegovy (semaglutide) — a GLP-1 receptor agonist, also injected once weekly. STEP trials showed average weight loss of approximately 15% of body weight.
- Saxenda (liraglutide) — a daily GLP-1 injection, the longest-established weight loss medication in the UK.
All three are prescription-only medicines requiring clinical assessment. You're typically eligible if you have a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes or high blood pressure. Use our free BMI calculator above to check where you fall, and our GLP-1 weight loss calculator can help estimate potential results at different doses.
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.
NHS vs Private Access and Next Steps
NHS access: Weight management medications are available through NHS specialist tier 3 weight management services, though you'll typically need a GP referral and may face waiting lists. Availability varies significantly by region. Private access: Available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber, without NHS waiting lists.
If you're taking sertraline and concerned about weight gain, discuss this with your GP. They can assess whether the sertraline is the primary cause, suggest dose adjustments if appropriate, or discuss whether you meet the eligibility criteria for prescription weight loss medication. Track your progress using our free progress tracker, and convert your weight between kg and stone using our weight converter for easy monitoring alongside your GP appointments.
- 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 sertraline cause weight gain?
Yes. Sertraline is an SSRI and can cause weight gain in some people, typically through increased appetite, water retention, or metabolic changes. Weight gain is listed as a common side effect affecting up to 1 in 10 people. If you've experienced weight gain since starting sertraline, discuss this with your GP — they may adjust your dose, switch medication, or offer additional weight management support.
Should I stop sertraline to lose weight?
No. Never stop sertraline without medical guidance, as stopping suddenly can cause withdrawal effects and your mental health condition may return. If sertraline's side effects are problematic, speak to your GP about alternatives or additional support. Weight management should never involve stopping essential mental health medication without professional oversight.
Can I take prescription weight loss medication if I'm on sertraline?
Possibly, but this requires individual assessment by a prescriber. There are no absolute contraindications between sertraline and GLP-1 medications like Mounjaro or Wegovy, but your prescriber will review all your medications and health conditions to ensure it's safe. Always inform any prescriber about all medicines you're taking, including sertraline.
What's the difference between Mounjaro and Wegovy for weight management?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist with average weight loss of 15–21%, whilst Wegovy (semaglutide) is a GLP-1 agonist alone with average weight loss around 15%. Both are once-weekly injections, prescription-only, and require clinical assessment. Results vary between individuals. Your GP or prescriber can discuss which might be more suitable for you.
What eligibility criteria apply for prescription weight loss medication in the UK?
You may be eligible if you have a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. Lower thresholds apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher health risks at lower BMI levels. Your GP can assess your individual eligibility.
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.