- Antidepressants help many people with depression, however, some do not seem to benefit as much. Currently, it is not possible to determine who will improve with certain antidepressants. Studies have shown that genes may influence whether an antidepressant works for an individual. Other studies have shown that depressed people tend to have lower levels of a chemical called glutamate in parts of their brain, and that glutamate levels increase after recovering from depression. Researchers want to study the antidepressant citalopram (Celexa) to see how it affects glutamate levels in the brain. They also want to study how a person s genes affect their response to this treatment.