Selective serotonin reuptake inhibitors (SSRIs) are among the most frequently prescribed medications for managing depression. These drugs influence the neurotransmitters, the chemicals that nerve cells in the brain use to communicate. When a neurotransmitter is released by one nerve cell, it is absorbed by other nerve cells. If it isn’t absorbed by other cells, it returns to the original cell in a process known as "reuptake." SSRIs function by blocking the reuptake of serotonin, which means more serotonin remains available for other nerve cells to absorb.As of 1999, the most commonly prescribed SSRIs were paroxetine (marketed as Paxil), fluoxetine (known as Prozac), and sertraline (branded as Zoloft). A study from that year found all three SSRIs to be similarly effective. The likelihood of patients switching from one type of medication to another was consistent across different drug classes, and there was no notable difference in how often patients switched from one SSRI to another or to a different type of medication, regardless of whether they began treatment with paroxetine (Paxil), fluoxetine (Prozac), or sertraline (Zoloft). While these SSRIs are equally effective, they are not interchangeable. Patients who do not tolerate one SSRI or do not respond well to it can often be successfully treated with a different SSRI. (Source: J Clin Psychiatry 1999;60:574-579.)