Zoloft (Sertraline hydrochloride) is a drug used for the treatment of depression, anxiety, and Is doxycycline a penicillin obsessive compulsive disorder (OCD). The exact mechanism that allows Zoloft to combat these affilictions Is doxycycline a penicillin still not completely understood. When taken regularly Zoloft increases the level of serotonin in the brain by inhibiting (not preventing) its breakdown. By blocking reuptake of serotonin, more remains available to affect brain receptors that control mood and behavior. Additionally, it has been seen that patients treated with Zoloft have been more likely to respond positively than those treated with placebos.