Basic mechanisms of antidepressant action

In general, antidepressants function by increasing the availability of monoamines (serotonin, noradrenaline, and/or dopamine) in the synapse; these monoamines are thought to be depleted in depression.¹

• SSRIs, SNRIs and TCAs achieve this by blocking one or more of the monoamine transporters, thus preventing the neurotransmitters from being taken back into the axon terminal that released them.¹
• MAOIs achieve this by inhibiting the activity of the monoamine oxidase enzyme (acting as an ‘enzyme inhibitor’) and thus preventing the breakdown of neurotransmitters.¹

Reference:

1.Stahl SM. Stahl’s Essential Psychopharmacology. Neuroscientific Basis and Practical Applications. 5th Edition. © Cambridge University Press, 2021.