In this video dr mayank agrawal is tailing about Ssri medicine SSRIs treat depression by increasing levels of serotonin in the brain. Serotonin is one of the chemical messengers (neurotransmitters) that carry signals between brain nerve cells (neurons). SSRIs block the reabsorption (reuptake) of serotonin into neurons. This makes more serotonin available to improve transmission of messages between neurons. SSRIs are called selective because they mainly affect serotonin, not other neurotransmitters.