Selective serotonin reuptake inhibitors (SSRIs) selectively block the reuptake of serotonin (5-HT) through their inhibiting effects on the sodium/potassium ATP-dependent serotonin transporter in presynaptic neurons. This increases the availability of 5-HT in the synaptic cleft. The main parameters to consider in choosing an antidepressant are side effects and safety. Most SSRIs are available generically and are relatively inexpensive. Older antidepressants, such as the TCAs and MAOIs usually require more visits and monitoring, and this may offset the low expense of the drugs. The SSRIs are relatively safe in overdose and better tolerated than the TCAs and MAOIs for most patients.