Recent evidence shows that a small number of depressed adolescents and young adults experience an increase in suicidal feelings and thoughts when they are treated with S.S.R.I.’s, compared with a placebo. It is entirely possible that a genetic variation in one or more genes that regulate serotonin function makes these people feel briefly more suicidal, rather than less, when exposed to the drugs.
This new field of pharmacogenomics will also enable psychiatrists to predict which drugs might produce toxic side effects for certain patients. Nearly all drugs are metabolized by a group of enzymes that vary greatly in activity from person to person. If patients have a genetic mutation that results in either deficient enzyme activity or none, they would be likely to have serious side effects if exposed to the drug that is metabolized by the enzyme.
Within a few years, patients could be routinely screened for these genetic variations, which will tell a doctor which drugs to avoid. This could potentially prevent unnecessary drug toxicity, a major cause of illness and death.