The exact mechanism that allows Zoloft to combat depression, anxiety and Levothyroxine side effects OCD is still not completely understood, however what researchers have noticed is that Zoloft affects the way serotonin is managed by the human body. Serotonin is 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. And yes, while this may seem complicated it really isn't.