Complex sentence: Serotonin reuptake inhibitors (SSRI) have been implicated in the induction of an "activation syndrome" (restlessness, labiality, etc.) that represent state change that fosters suicidality in people under age 25 during the initial weeks of treatment.
Split into simpler sentences: Serotonin reuptake inhibitors (SSRI) have been used in the induction of an "activation syndrome" (restlessness, labiality, etc.). The syndrome generally represents a state change that encourages suicidal tendencies in people under age 25 during the initial weeks of treatment.