A 54-year-old woman presented with severe anxiety, multiple somatic complaints, medication intolerance and adverse drug reactions (ADRs) to numerous prescribed psychotropic medications. Multiple drug metabolizing deficiencies were suspected. Molecular analysis was performed for the CYP2 family of Cytochrome P450 (CYP450) drug metabolism isoenzymes by DNA typing CYP2D6, CYP2C9, and CYP2C19 genes. A multiple deficiency in CYP2 drug metabolism was discovered. The patient was a double carrier of null alleles for CYP2D6, a carrier of a null allele for CYP2C19 and a carrier of a deficient allele for CYP2C9. These alleles were confirmed by Mendelian inheritance in her nuclear family, where her brother had a similar multigene CYP2 deficiency. The patient improved clinically with discontinuation of psychotropic medications, suggesting that much of her symptomatology was drug-induced. DNA typing for multigene CYP2 deficiencies is diagnostically useful in individuals with histories of multiple ADRs, which could be avoided by DNA-guided individualized prescription.