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
Prozac and Weight Loss — What You Need to Know
Prozac (fluoxetine) is an antidepressant that can sometimes influence weight as a side effect, but it's not a weight loss medication. If you're looking for prescription weight management options in the UK, there are licensed alternatives specifically designed for weight loss. This guide explains how antidepressants like Prozac affect weight, and what evidence-based weight loss medications are available to eligible adults through the NHS or private prescribing.
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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 Weight Loss Medications Available Now
If weight management is your primary health goal, the UK has three prescription-only weight loss medications licensed specifically for this purpose. These are very different from antidepressants like Prozac:
- Mounjaro (tirzepatide) — A dual GIP and GLP-1 receptor agonist. Once-weekly injection. In clinical trials, helped people lose an average of 15–21% of their body weight alongside diet and exercise.
- Wegovy (semaglutide) — A GLP-1 receptor agonist. Once-weekly injection. Clinical trials showed average weight loss of around 15% body weight.
- Saxenda (liraglutide) — A GLP-1 agonist. Daily injection. Effective for weight management in eligible adults.
All three require a prescription from a UK-licensed prescriber and a clinical assessment to confirm you're eligible. Eligibility generally requires a BMI of 30 or above, or 27 or above with weight-related health conditions. Results vary between individuals, and medications work best alongside a reduced-calorie diet and increased physical activity.
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.
Getting Weight Loss Help in the UK — Your Next Steps
If you're concerned about your weight or want to explore prescription weight loss options, your GP is the best starting point. They can discuss whether you meet NHS eligibility criteria and refer you to specialist weight management services if appropriate.
You can also calculate your BMI using our free BMI calculator to understand your current weight category. Many eligible adults access prescription weight loss medications through private prescribing services, which offer an alternative to NHS waiting lists. A licensed prescriber will assess your health, confirm eligibility, and issue a prescription if suitable. Always discuss any weight management plan with your GP, especially if you're currently taking other medications like Prozac.
- 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.
Does Prozac cause weight gain or weight loss?
Prozac can affect weight differently in different people. Some people experience weight loss (especially early in treatment), while others gain weight over time. Weight changes are a known side effect of many antidepressants. If you're concerned about weight changes on Prozac, discuss this with your GP — they may adjust your dose or explore alternatives.
Can I use weight loss injections if I'm taking Prozac?
Weight loss medications like Mounjaro and Wegovy can potentially interact with other medicines. Always inform your prescriber that you're taking Prozac before starting any weight loss treatment. Your GP or licensed prescriber will assess whether it's safe to use both medications together.
What's the difference between Prozac and weight loss medications?
Prozac is an antidepressant (SSRI) used to treat depression and anxiety — weight changes are a side effect, not the intended effect. Mounjaro, Wegovy, and Saxenda are specifically licensed for weight management and work by affecting appetite hormones. They serve completely different medical purposes.
How do I know if I'm eligible for prescription weight loss medication in the UK?
Generally, you're eligible if you have a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes or high blood pressure. Use our free BMI calculator to check your current BMI, then discuss eligibility with your GP or a licensed prescriber.
What's the difference between NHS and private weight loss medication access in the UK?
NHS access goes through specialist tier 3 weight management services, often with waiting lists. Private prescribing allows faster access through GPhC-registered online services, though there's a cost. Both routes require a clinical assessment and prescription from a UK-licensed prescriber.
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.