The differences in the genetic structures involved in the metabolism of drugs are effective on the efficacy and side effects of the drug. With the genetic tests currently being applied, drug sensitivities and effective treatments in cancer patients can be determined in advance.

As a result of genetic investigations in hematological diseases such as leukemia and lymphoma, the type of treatment to be applied in patients can be determined. Anti-EGFR treatment (tyrosine kinase inhibitor drugs and monoclonal antibodies) (imatinib, gefinib, erlotinib, sunatinib, etc.), which is one of the newest treatment protocols, is already known and it is possible to increase the chance of responding to treatment.

Prior to the use of warfarin (Kumadin) and clopidogrel (Plavix) drugs, medication sensitivities can be predetermined. For the drugs determined to be toxic, dose adjustments can be made or alternative medications are preferred and the patients can be prevented from unwanted side effects.

In addition, almost all drugs used in the treatment of depression are metabolised by CYP2D6 and CYP2C19 enzymes in the liver. It also affects 5HTT, CYP1A2 and NAT2 enzymes that are commonly prescribed and are given the response to antidepressant drugs called A serotonin selective reuptake inhibitors (SSRIs)