How do antidepressant medications work on the brain?

Nobody knows.: Nobody knows for sure. Most antidepressants influence brain neurotransmitters like serotonin, nor Epinephrine and dopamine. These brain messengers have a role in maintaining a normal mood but how they really work remains a mystery. About a third of our patients respond poorly to antidepressants so we need to look for medications that influence other neurobiological systems.

Addendum: A current working hypothesis is that due to the effects colleagues have discussed, signalling within nerve cella is enhanced. Therefore when signals from many nerve cells are combined by a receiving cell, its subsequent output response is amplified. (sort of like a digital sound amplifier.) in depression, these output signals are muffled.

Neurotransmission: Antidepressant medications act on enzymes, receptors, and neurotransmitters in various parts of the brain to modulate the functioning of circuitry that affects mood, thinking, sleeping, anxiety and the ability to think and concentrate. Each medication is a bit different, and they are separated into classes depending on their affects on the brain circuits. The results are to normalize functioning.