Ans. D: FluoxetineThe two medications proven to be most effective in the treatment of OCD are tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs).Serotonin is a chemical in the brain called a neurotransmitter that may be imbalanced in people with OCD.While both drugs are very effective, SSRIs have generally become the preferred medication for anxiety disorders including OCD.SSRIs have less side effects than other forms of antidepressants, less withdrawal symptoms, less danger in the event of an overdose and overall are considered safer that other types of drugs (TCAs and SSRIs are both very safe drugs, however). Common SSRIs include fluoxetine, fluvoxamine, seraline, paroxetine, citalopram, and escitalopram.