Zoloft is designed to help those who suffer from depression, Levothyroxine dosage anxiety, Levothyroxine dosage or obsessive compulsive disorder. It is part of a class of drugs called selective serotonin reuptake inhibitors. The mechanism by which Zoloft works is not fully understood although what researchers do know is that it works by increasing the level of serotonin in the brain by inhibiting its breakdown.