Zoloft is an antidepressant that is used to treat depression, Levothyroxine bnf anxiety and obsessive compulsive disorder. It is a selective serotonin reuptake inhibitor (SSRI) which help to increase the amount of serotonin available in the brain. Zoloft produces fewer side effects than older antidepressants called tricyclics, Levothyroxine bnf such as Elavil and Tofranil.