Zoloft (or sertraline HCL) is used for the treatment of depression, obsessive compulsive disorder and excessive anxiety. It affects the way that serotonin is managed by the body; serotonin being a chemical that is part of an important drug family known as selective serotonin re-uptake inhibitors (or SSRI's). By modifying the levels of serotonin in the brain, SSRI's help to combat certain afflictions such as depression, excessive anxiety and obsessive compulsive disorder.In a professional tone: The exact mechanism that allows Zoloft to combat these affilictions is still not completely understood, however what researchers have noticed is that Zoloft affects the way that serotonin is managed by the human body. Serotonin Is doxycycline a penicillin part of a drug family known as selective serotonin re-uptake inhibitors (or SSRI's). SSRI's increase the level of serotonin in the brain by inhibiting (not preventing) its breakdown.