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.
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.
Hoping to make the drugs more targeted and reduce side effects, scientists began studying existing antidepressants to figure out which specific monoamines were most associated with improvements in depression.
We're also not sure why antidepressants work the way they do: they change monoamine levels within a few hours of taking the medication, but patients usually don't feel the benefit until weeks later.