These two so-called " antidepressants" blocked the usual depletion of the catecholamines dopamine and norepinephrine and blocked the depletion of the monoamine serotonin.
Very similarly, there are medications like selegiline which inhibits monoamine oxidase B, also known as MAO-B, which is another enzyme that metabolizes dopamine.
In the 1970s, several different researchers converged on an answer: the most effective antidepressants all seemed to act on one monoamine called serotonin.
Most antidepressants to date have been based on the monoamine hypothesis, which holds that depression is caused by low levels of a class of chemical messengers.
The discovery of these antidepressant drugs gave rise to the chemical imbalance theory, the idea that depression is caused by having insufficient monoamines in the brain's synapses.