In the last decades, the treatment of obsessive-compulsive disorder (OCD) has been revolutioned by the introduction into the clinical practice of the selective serotonin (5-HT) reuptake inhibitors (SSRIs), following the observation of the unique response of OCD patients to clomipramine. However, if with no doubt the 5-HT system is central to the pharmacological treatment of OCD, it is unlikely that it represents the whole story. In fact, different studies suggest abnormalities of other neurotransmitters, neuropeptides or second messengers, so that it can be hypothesized that the possible heterogeneity of pathophysiological mechanisms might underlie the different clinical pictures and responses to treatment. Moreover, latest developments in the pharmacology of SSRIs have shown that they share the common property of 5-HT reuptake blockade, but, with the exception of citalopram and escitalopram, they do interact with other receptors and systems. In this paper, the latest findings on pharmacological treatments of OCD will be reviewed, together with a focus on putative targets for future drugs, such as the glutamate system or second messengers, and the problems related to treating OCD in different ages.