Book excerpt: Fluoxetine, best known by the trade name Prozac®, unlike other psychotropic drugs whose effects were serendipitously stumbled upon, was the first developed for a precise mechanism of action, that is, the ability to selectively inhibit serotonin reuptake, based upon the theory that increasing the availability of serotonin would treat major depression. Once approved by the FDA in 1987, fluoxetine quickly became the most prescribed psychotropic drug worldwide and its success in improving mood disorders has triggered the development of a large number of congener molecules, commonly known as SSRIs after their purported mechanism of action. However, a quarter of a century after its development, the idea that fluoxetine asserts its positive behavioral effect through inhibition of serotonergic reuptake is not firmly established. This book reviews several preclinical and clinical reports suggesting that the pharmacological effects of fluoxetine may be mediated by means other than the regulation of serotonin, including the regulation of gene expression, modifying epigenetic mechanisms as well as modifying microRNAs. One of the most prominent mechanisms for the therapeutic relevance of fluoxetine relates to influencing neuroplasticity by enhancing neurotropic factors, including BDNF signaling and altering adult neurogenesis. The ability of fluoxetine to rapidly increase neurosteroid levels accounts for the fast anxiolytic effects of this drug. Fluoxetine action at sigma-1 receptor or modulating glutamatergic neurotransmission as well as the combination of fluoxetine with other psychotropic drugs is discussed in relation to its therapeutic effects. While fluoxetine was primarily prescribed as an antidepressant, this drug currently represents a treatment of choice for a broad spectrum of psychiatric disorders, including post-traumatic stress disorder and a range of anxiety disorders. This drug even possesses analgesic actions and is a valuable therapy for stroke. This book also highlights emerging evidence on the gender-specific effects of fluoxetine, its potential adverse features, including its addiction liability in combination with psychostimulants, and the impact of perinatal fluoxetine exposure.