SB-649,915 is a serotonin reuptake inhibitor and 5-HT<sub>1A</sub> and 5-HT<sub>1B</sub> receptor antagonist which is being investigated for its antidepressant effects. Relative to the selective serotonin reuptake inhibitors (SSRIs), SB-649,915 has a faster onset of action and may also have greater clinical efficacy as well. This can be attributed to blockade of 5-HT<sub>1A</sub> and 5-HT<sub>1B</sub> autoreceptors which inhibit serotonin release.