Fluoxetine on Emotional Experience (FLEX) Study

Inclusion Criteria: * 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 Exclusion Criteria: 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); * 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.