The effect of selective serotonin reuptake inhibitors (SSRIs) on the circadian light response

INTERVENTION: Participants will be asked to attend 4 test sessions of 5 hours each, with one week between each session. Each session commences 4 hours before the participants' habitual bedtime, concluding 1 hour after. The first two sessions will be dim‐light exposures (<1 lux), with citalopram 30mg being administered on the first evening, and placebo on the second. The first evening serves to confirm that citalopram 30mg does not influence absolute levels of melatonin, which would impede our ability to measure the suppression of melatonin during the following light exposures. The second night serves as a dark‐control for subsequent light exposures. The final two nights are light exposures ( 100 lux) with participants being randomised to receive either citalopram 30mg, or placebo, first. Each participant will be exposed to both conditions. A single capsule of citalopram 30mg (or matched placebo) will be administered in the laboratory 4 hours prior to each participants' bedtime according to their sleep‐wake schedule. This takes place during all in lab sessions. CONDITION: Major Depressive Disorder (MDD) PRIMARY OUTCOME: Alertness Testing: Objective and Subjective. ; ; Objective alertness is assessed via an auditory psychomotor vigilance task. ; ; Subjective alertness is assessed every 60 minutes using the Karolinska Sleepiness Scale Salivary melatonin levels SECONDARY OUTCOME: ‐ INCLUSION CRITERIA: Healthy Caucasian males and females