Depression - Major Depressive DisorderFLEXNCT07424781
Fluoxetine on Emotional Experience (FLEX) Study
A study testing Fluoxetine in people with Depression - Major Depressive Disorder and Irritability, run by University of Oxford at 1 site in United Kingdom.
Trial summary
The goal of this clinical medicine study is to investigate how does antidepressant fluoxetine modulate anger processing in healthy young people . The main questions it aims is to answer are: 1. How does fluoxetine affect responses to anger-related stimuli such as words, faces, and autobiographical recall? 2. Read more about this study
- Who is it for?
- Ages 18 to 24 yearsHealthy volunteers can take part
- Conditions the study is for
- Depression - Major Depressive Disorder, Irritability, Depression
- What is being tested?
- Fluoxetine
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 80 participants
- Where
- 1 siteUnited Kingdom
- Study dates
- 1 Oct 2025to 31 Dec 2026
- Phase
- Interventional
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 24 years
- All sexes
- Healthy volunteers accepted
- Adult
Who may be able to join
- Be aged 18-24 years (inclusive)
- Be resident in the UK for the duration of the study
- Have normal or corrected to normal vision
- Participant is willing and able to give informed consent for participation in the research
- Sufficiently fluent English to understand and complete the study
Who cannot join
- The participant may not enter the study if ANY of the following apply:
- Psychiatric History:
- Current or past diagnosis of any psychiatric disorder, as determined by the Structured Clinical Interview for the DSM-5 (SCID-5) and self-report. This includes, but is not limited to, depression, anxiety disorders, alcohol or drug dependency, personality disorders, suicidal ideation, and other psychiatric conditions;
- First degree relative with a diagnosis of mania;
- Lifestyle:
- Heavy smoker or vaper (> 10 cigarettes per day, or >2 mL e-liquid, or >15mg/day from a nicotine patch);
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- Heavy use of caffeine (drink > 4 of 250ml cups/cans of coffee or energy drinks per day);
- Heavy drinker (drink >14 standard alcoholic drinks per week);
- Current or recent use (in the last 3 months) of any psychoactive substance according to self-report and a urine drug test screening for recent use of 10 common recreational substances;
- Physical Health:
- Severely underweight or overweight in a manner that renders them unsuitable for the study in the opinion of the study medical advisor;
- Known contraindication to fluoxetine, such as hypersensitivity to fluoxetine or any component in its formulation;
- Pregnancy, as determined by a urine pregnancy test or plans to become pregnant within the next 3 months;
- Breastfeeding;
- Not able to consume gelatine;
- Medical History:
- Past or ongoing health issue which, in the opinion of the study medical advisor, may interfere with the safety of the participant or the scientific integrity of the study, including but not limited to: seizures or epilepsy, heart rhythm problem, renal disease, hepatic disease, glaucoma, diabetes, bleeding disorders or clotting conditions (e.g., haemophilia, thrombocytopenia);
- Diagnosis of a significant neurological condition (e.g., epilepsy, multiple sclerosis, traumatic brain injury).
- Diagnosis of a neurodevelopmental condition, such as autism spectrum disorder (ASD) or attention-deficit/hyperactivity disorder (ADHD);
- Current or recent use of medication that might interfere or interact with the effects of fluoxetine, in the opinion of the study medical advisor, including but not limited to: monoamine oxidase inhibitors (MAOIs), medications affecting serotonin levels (e.g., tramadol, triptans, St. John's Wort), anticoagulants or blood thinners (e.g., warfarin), anti-inflammatory medications (e.g., aspirin, ibuprofen), or medications known to affect heart rhythm;
- Prior Study Participation:
- Participation in any other psychological or medical experiment involving taking any kind of drug/medication/vaccine, within the last 3 months;
- Participation in any other study involving the current or similar tasks, within the last 6 months;
- Others
- •Any other significant finding which may arise during the screening process and which, in the opinion of the Principal Investigator/medical advisor, may influence the scientific integrity of the study, or the participant's ability to participate in the study.
Trial locations and contacts
1 site in 1 country. Contact the study team or a site near you to ask about taking part.
United Kingdom1 site, 1 recruiting
- Recruiting
Department of Psychiatry, University of Oxford
Oxford, Oxfordshire, OX3 7JX
Ye Wo, MSc, 07564300004, ye.wo@psych.ox.ac.uk
About this study
Official title: The Effect of Fluoxetine Treatment on Anger Processing in Healthy Young People
The goal of this clinical medicine study is to investigate how does antidepressant fluoxetine modulate anger processing in healthy young people . The main questions it aims is to answer are:
- How does fluoxetine affect responses to anger-related stimuli such as words, faces, and autobiographical recall?
- How does fluoxetine influence responses during frustration induction in frustrative non-reward and threat paradigms?
- Does the effect manifest in physiological markers, including heart rate variability and facial expressions?
Read more
Researchers will compare fluoxetine to a placebo to see if drug fluoxetine affects anger processing.
Participants will:
Take 20mg fluoxetine or a placebo every day for 7 days. Visit the university site for questionnaire and tasks assessments. Heart rate variability and facial expressions will be recorded in some of the tasks.
- Being tested
- Fluoxetine, Placebo
- Keywords
- depression, young people, fluoxetine, irritability, anger
- Medical subject headings
- Depression
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
FluoxetineDrug
Participants will receive 20mg of fluoxetine daily for 7 days. Tablets encapsulated to aid blinding.
PlaceboDrug
Participants will receive one dose placebo (sucrose) daily for 7 days. Tablets encapsulated to aid blinding.
| Study group | Role | What they receive |
|---|---|---|
| fluoxetine | Active comparator | Participants will be taking 20mg fluoxetine daily. Receives: Drug: Fluoxetine |
| placebo | Placebo comparator | Participants will be taking one placebo capsule daily. Receives: Drug: Placebo |
What is being measured
The primary outcome is the main question the study is designed to answer.
Behavioral Measure: Facial Expression Recognition Task (FERT)
Recognition of angry faces in the Facial Expression Recognition Task
Measured: On the last day of the 7-day treatment
Secondary outcomes (8)
Behavioural Measure: The Affordances Task
Performance on an affordances task in which participants have to decide to fight or escape under threatening situations with different environmental affordance conditions.
Measured: On the last day of the 7-day treatment
Behavioural Measure: Emotional Categorization Task (ECAT)
Performance on recognising and memorising anger related words in the Emotional Categorization Task (ECAT)
Measured: On the last day of the 7-day treatment.
Performance on Carnival Task
Performance on an anger induction task in which the study's rigged design creates frustrating non-reward responses.
Measured: On the last day of the 7-day treatment.
Subjective Measure: Rest Task
Participants' rating of anger-related emotions during a resting task.
Measured: On the last day of the 7-day treatment.
Subjective Measure: Anger Memory Recall Task
Participants' ratings of anger-related emotions and bodily sensations during a task that involves guided imagery of a past personal experience.
Measured: On the last day of the 7-day treatment.
Physiological Measure: Heart Rate Variability
Heart rate variability measures across a battery of anger-induction tasks.
Measured: On the last day of the 7-day treatment.
Physiological Measure: Facial Expression
Video recordings that identify facial expressions across a battery of anger-induction tasks.
Measured: On the last day of the 7-day treatment.
Behavioural measure: Emotional Recognition Memory Task (EMEM)
Description: Performance on recognising and memorising anger related words in the Emotional Recognition Memory Task (EMEM).
Measured: On the last day of the 7-day treatment.
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted20 Feb 2026
- Study start1 Oct 2025
- Primary completion31 Dec 2026 (estimated)
- Study completion31 Dec 2026 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Depression - Major Depressive DisorderStudies of the same condition, open and under way.
- More trials run by University of OxfordThe sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Model description
- Participants will be assigned to receive either fluoxetine or placebo. Fluoxetine is not being administered for treatment purposes, the purpose is to understand the mechanisms underpinning its effects.
- Masking
- Triple blind
- Who is masked
- Participant, Investigator, Outcomes assessor
- Enrolment
- 80 participants (estimated)
Sponsor and investigators
- Lead sponsor
- University of Oxford
- Sponsor type
- University, hospital or other
- Collaborators
- Wellcome Trust, National Institute for Health Research, United Kingdom
- Responsible party
- Principal investigator, Catherine Harmer, University of Oxford
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07424781
- Sponsor's protocol ID
- MS IDREC 1017147
- Acronym
- FLEX
- Status last verified
- Sep 2025
- First submitted
- 3 Dec 2025
- Last updated
- 20 Feb 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Yes: Data which has been fully de-identified and relevant supporting materials (e.g., study protocol, data dictionary, and analysis documentation) may be shared with other academic organisations in the future, including those outside of the UK and the EU. Participants will be informed of this and specific consent to this is obtained within the Informed Consent Form.
Study at a glance
From the registry record, last updated by the sponsor on 20 Feb 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- The Effect of Fluoxetine Treatment on Anger Processing in Healthy Young People
- ClinicalTrials.gov ID
- NCT07424781
- Acronym / sponsor ID
- FLEX / MS IDREC 1017147
- Keywords
- depression, young people, fluoxetine, irritability, anger
- Study type
- Interventional
- Recruitment status
- Recruiting
- Enrolment
- 80 participants (estimated)
- Lead sponsor
- University of OxfordUniversity, hospital or other
- Collaborators
- Wellcome Trust, National Institute for Health Research, United Kingdom
- Study start
- 1 Oct 2025 (actual)
- Primary completion
- 31 Dec 2026 (estimated)
- Study completion
- 31 Dec 2026 (estimated)
- First posted
- 20 Feb 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
The goal of this clinical medicine study is to investigate how does antidepressant fluoxetine modulate anger processing in healthy young people . The main questions it aims is to answer are:
- How does fluoxetine affect responses to anger-related stimuli such as words, faces, and autobiographical recall?
- How does fluoxetine influence responses during frustration induction in frustrative non-reward and threat paradigms?
- Does the effect manifest in physiological markers, including heart rate variability and facial expressions?
Researchers will compare fluoxetine to a placebo to see if drug fluoxetine affects anger processing.
Participants will:
Take 20mg fluoxetine or a placebo every day for 7 days. Visit the university site for questionnaire and tasks assessments. Heart rate variability and facial expressions will be recorded in some of the tasks.
Study design
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Triple blind (participant, investigator, outcomes assessor)
- Number of arms
- 2
- Model description
- Participants will be assigned to receive either fluoxetine or placebo. Fluoxetine is not being administered for treatment purposes, the purpose is to understand the mechanisms underpinning its effects.
| Arm | Type | Receives |
|---|---|---|
| fluoxetine | Active comparator | Drug: FluoxetineParticipants will be taking 20mg fluoxetine daily. |
| placebo | Placebo comparator | Drug: PlaceboParticipants will be taking one placebo capsule daily. |
Who may qualify
- Ages
- 18 to 24 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult
Key inclusion criteria (5 listed)
- Be aged 18-24 years (inclusive)
- Be resident in the UK for the duration of the study
- Have normal or corrected to normal vision
- Participant is willing and able to give informed consent for participation in the research
- Sufficiently fluent English to understand and complete the study
Key exclusion criteria (25 listed)
- Current or past diagnosis of any psychiatric disorder, as determined by the Structured Clinical Interview for the DSM-5 (SCID-5) and self-report. This includes, but is not limited to, depression, anxiety disorders, alcohol or drug dependency, personality disorders, suicidal ideation, and other psychiatric conditions;
- First degree relative with a diagnosis of mania;
- Heavy smoker or vaper (> 10 cigarettes per day, or >2 mL e-liquid, or >15mg/day from a nicotine patch);
- Heavy use of caffeine (drink > 4 of 250ml cups/cans of coffee or energy drinks per day);
- Heavy drinker (drink >14 standard alcoholic drinks per week);
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| FluoxetineParticipants will receive 20mg of fluoxetine daily for 7 days. Tablets encapsulated to aid blinding. | Drug | fluoxetine |
| PlaceboParticipants will receive one dose placebo (sucrose) daily for 7 days. Tablets encapsulated to aid blinding. | Drug | placebo |
Primary outcome
Behavioral Measure: Facial Expression Recognition Task (FERT)
Time frame: On the last day of the 7-day treatment
Recognition of angry faces in the Facial Expression Recognition Task
8 secondary outcomes
Behavioural Measure: The Affordances Task
Time frame: On the last day of the 7-day treatment
Behavioural Measure: Emotional Categorization Task (ECAT)
Time frame: On the last day of the 7-day treatment.
Performance on Carnival Task
Time frame: On the last day of the 7-day treatment.
Subjective Measure: Rest Task
Time frame: On the last day of the 7-day treatment.
Subjective Measure: Anger Memory Recall Task
Time frame: On the last day of the 7-day treatment.
Physiological Measure: Heart Rate Variability
Time frame: On the last day of the 7-day treatment.
Physiological Measure: Facial Expression
Time frame: On the last day of the 7-day treatment.
Behavioural measure: Emotional Recognition Memory Task (EMEM)
Time frame: On the last day of the 7-day treatment.
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 20 Feb 2026.
- Individual participant dataSharing planned: Yes. Data which has been fully de-identified and relevant supporting materials (e.g., study protocol, data dictionary, and analysis documentation) may be shared with other academic organisations in the future, including those outside of the UK and the EU. Participants will be informed of this and specific consent to this is obtained within the Informed Consent Form.
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Fluoxetine in people with Depression - Major Depressive Disorder and Irritability, run by University of Oxford at 1 site in United Kingdom.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 5 inclusion and 25 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: looking for participants now, as of the sponsor's last update on 20 Feb 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in United Kingdom. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. Some participants in this study may receive a placebo. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Catherine Harmer, PhD (+441865 618326, catherine.harmer@psych.ox.ac.uk), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Behavioral Measure: Facial Expression Recognition Task (FERT) (time frame: On the last day of the 7-day treatment). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 20 Feb 2026.