Zoloft (sertraline) hydrochloride is an antidepressant used to treat depression, panic disorder and Flagyl obsessive-compulsive disorder (OCD). It belongs to the class of drugs called selective serotonin reuptake inhibitors (SSRIs), which block the reabsorption of serotonin by certain nerve cells in the brain. As a result, this helps boost the levels of serotonin available in the brain.