Drug therapies are based on the assumption that drugs can cure a neurochemical imbalance, which is seen as the cause of OCD. Two types of drug are used for the treatment of OCD: antidepressants and anti-anxiety drugs. SSRIs (antidepressants) increase the level of serotonin in the synapse and result in more serotonin being received by the receiving cell, thus reducing the symptoms of OCD.