SSRI stands for selective serotonin reuptake inhibitor, which is just another name for modern antidepressants that help the body release more serotonin into the gaps between brain cells. Antidepressants that help the body release serotonin and norepinephrine are called SNRIs, which stands for serotonin and norepinephrine reuptake inhibitors. Some authorities are using the term DRIs for double reuptake inhibitors and TRIs for triple reuptake inhibitors to describe antidepressants that stimulate the release of two or three of the neurochemicals serotonin, norepinephrine, and dopamine. Because they act differently, antidepressants all feel different and are more effective for some individuals than others.
In general, serotonin decreases depression, anxiety, aggression, and sleep, while increasing appetite and weight gain. Serotonin antidepressants usually prolong the time to reach orgasm. Most modern antidepressants have a strong serotonin effect.
Norepinephrine generally increases physical energy, motivation, and anxiety, while decreasing appetite, weight, and sleep.
Dopamine tends to increase alertness, concentration, and optimism, while decreasing appetite.