RecruitingNAINTERVENTIONAL

Fluoxetine on Emotional Experience (FLEX) Study

The FLEX Study wants to understand how fluoxetine, a medication often used for depression, affects how healthy young people aged 18-24 process anger. Researchers are exploring if this medication changes reactions to anger-related words and faces, or how people respond when things are frustrating. They'll also check if these changes show up in body signals, like heart rate. Participants will take either fluoxetine or a placebo (a dummy pill) for 7 days, then visit a university for some tasks and questionnaires. The aim is to see if fluoxetine has an impact on how we experience and react to anger.

At a glance

Status

Recruiting

Phase

Sponsor

University of Oxford

Enrolment target

Start

01 Oct 2025

Estimated completion

31 Dec 2026

Depression - Major Depressive Disorder Irritability Depression

What is this study about?

The FLEX (Fluoxetine on Emotional Experience) Study is a and important piece of research looking into how a common medicine called fluoxetine affects anger. Fluoxetine is often prescribed for conditions like depression, but this study is focusing on healthy young people aged 18 to 24 to get a clearer picture of its effects on anger specifically. The main goal is to understand if taking fluoxetine changes how someone experiences and deals with feelings of anger.

Researchers will be looking at a few key things. For example, they'll see how participants respond to angry-looking faces or words linked to anger. They'll also put people in situations designed to be a bit frustrating to see if the medication changes their reaction. Beyond just feelings, the study will also check to see if these changes show up in physical ways, like how their heart rate changes or what their facial expressions show. This helps researchers get a complete picture of fluoxetine's impact.

To figure this out, some participants will take fluoxetine, while others will take a 'placebo' – a pill that looks the same but contains no medicine. Comparing these two groups helps the researchers know if any changes they see are actually due to the fluoxetine or something else. This research is important because understanding how medicines like fluoxetine affect different emotions, even in healthy individuals, can help us learn more about how they work and potentially help people who struggle with anger.

Key takeaways

This study explores how fluoxetine affects anger in healthy young adults.
Participants take either fluoxetine or a dummy pill for 7 days.
Assessments include questionnaires, tasks, and body measurements like heart rate.
The research aims to understand fluoxetine's impact on emotional responses.
Participation involves short-term medication and a university visit for tests.

Who may be eligible?

To join this study, you need to be a healthy young person between 18 and 24 years old and living in the UK. You should also have good eyesight (with or without glasses/contact lenses) and be able to understand and speak English well enough to take part in all the study activities. Most importantly, you need to be willing to give your informed consent, which means you understand what the study involves and agree to take part.

There are several reasons why you might not be able to join. If you have ever been diagnosed with a mental health condition like depression, anxiety, or issues with alcohol or drugs, or if you have struggled with suicidal thoughts, you can't participate. Also, if a close family member (like a parent or sibling) has ever been diagnosed with mania (a very high mood), this study might not be suitable for you. You also cannot be a heavy smoker, vaper, or heavy user of caffeine or alcohol, as these can affect how your body and mind respond.

Certain health conditions or medications would also mean you can't join. For instance, if you have a known allergy to fluoxetine, have a history of seizures, heart problems, kidney or liver disease, or if you are pregnant, breastfeeding, or planning to become pregnant soon, you would not be eligible. If you're not sure about any of these points, the study team will be able to help you figure it out.

Quick self-check

Are you between 18 and 24 years old?
Do you live in the UK?
Do you have normal or corrected vision?
Are you able to speak and understand English well?
Have you ever been diagnosed with any mental health condition?
Are you currently pregnant, breastfeeding, or planning to be pregnant in the next 3 months?

This is a guide only — the research team will confirm whether you can take part.

What does participation involve?

If you decide to take part in this study, you will be asked to visit the university study site. You will be given either a 20mg fluoxetine pill or a dummy pill (placebo) to take once a day for 7 days. It's important that you take the pill every day as instructed. After these 7 days, you will attend another session at the university. During this visit, you will complete some questionnaires and take part in various tasks on a computer or other devices. Some of these tasks will involve measuring your heart rate and recording your facial expressions. The entire study involves taking the medication for one week and then attending the assessment sessions, which will be carefully explained to you beforehand.

Potential risks and benefits

Taking part in this study may offer you the satisfaction of contributing to medical research and helping scientists understand more about how medication affects emotions. You will receive very careful medical checks to see if you are healthy enough to take part. As with any medication, there's always a chance of side effects from fluoxetine, though the dose in this study is low and it's only taken for a short period. Potential side effects can include feeling sick, headaches, or feeling anxious, but these will be fully explained to you. You will also go through a urine test for drugs and a pregnancy test if you can become pregnant. You are free to withdraw from the study at any time, for any reason, without it affecting your medical care.

Locations (1)

Department of Psychiatry, University of Oxford
Oxford, United Kingdom· Recruiting

Common questions

What is fluoxetine?

Fluoxetine is a medicine commonly used to treat depression, anxiety, and other conditions. It's also known by its brand name, Prozac.

Why are you studying anger in healthy people?

By studying healthy people, researchers can better understand the basic effects of fluoxetine on anger without other medical conditions complicating the results.

Will I know if I'm taking the real medicine or the dummy pill?

No, it's a 'blinded' study, meaning neither you nor the research team will know until the study is over. This helps ensure fair results.

How long will I have to take the study medication?

You will take the study medication (either fluoxetine or a placebo) once a day for just 7 days.

What happens after the 7 days of taking the pill?

You will visit the university study site for a series of tasks and questionnaires, and to have some physical responses measured like heart rate and facial expressions.

How to find out more

Catherine Harmer, PhD

catherine.harmer@psych.ox.ac.uk +441865 618326 Official trial record

Always speak to your GP or specialist before deciding to take part in a study.