Finding the right medication in psychiatry can be very demanding both for the doctor and for the patient. It becomes extremely grueling when the patient has a rare type of metabolizing enzymes, and many drugs may be ineffective or cause side effects.

To highlight the therapeutic difficulties in psychiatric treatment of the patient with complex genetic cytochrome P450 system alterations.

To provide an example on a complicated treatment course of the patient that is poor CYP2D6 and ultrarapid CYP2C19 metabolizer.

Literature review in scientific database–Pubmed–and case report presentation.

We report a case of a woman in her early twenties who was repeatedly referred for psychiatric treatment. A diagnosis of paranoid schizophrenia was established, but all treatment rounds were unsuccessful, the illness kept progressing, and major depressive disorder aggravated the clinical picture. The patient became suicidal and injured herself. During the sixth hospitalization in one year the CYP2D6, CYP2C19 and CYP2C9 genotyping was done. CYP2C19 ultrarapid (*1/*17) and CYP2D6 poor metabolizer (*4/*5) profile was discovered. Drugs, that should have been avoided due to the patient's genetic profile, had been prescribed throughout five hospitalizations in a row.

As ultrarapid CYP2C19 metabolizers compose around 3–4% and poor CYP2D6–6–10% of Caucasians, this case presents a rare genetic variant that only 0.18–0.4% of Caucasian population may have. These cases can be extremely clinically challenging and affect healthcare outcomes and costs. Further studies that would include clinical effectivity, drug concentration and genetic testing results are needed.