Psychiatric Drug-Drug Interactions

A Refresher

Tammie Lee Demler, BS, PharmD, MBA, BCPP


US Pharmacist. 2012;37(11):HS-16-HS-19. 

In This Article

Abstract and Introduction


The vast increase in the number of new psychopharmacologic agents has made more therapeutic options available, but it has also complicated patient treatment. Combination therapy used in psychiatric practice makes drug interactions more likely and increases the risk of adverse outcomes to patients. The amount of information on drug-drug interactions is overwhelming, so health systems have implemented the use of computer software to assist in the detection of these problematic combinations. While these systems offer necessary support, the pharmacist's expertise in triaging these alerts and communicating the relevance to the prescriber is essential. This review will provide an essential refresher on psychiatric drug interactions for institutional practitioners as well as offering suggestions to optimize patient safety when patients are on medication regimens that include psychiatric drugs.


The vast increase in the number of new psychopharmacologic agents over the last 20 years has made more therapeutic options available, but it also has made treating patients more complicated. Prescribing practices, which include the concurrent administration of a variety of psychotropic drugs, have made the risk of drug-drug interactions more likely. Drug interactions are known to play a significant role in the incidence of adverse drug reactions (ADRs) both in the community and in hospitals. Reducing ADRs is a critical element in providing safe medication use for hospitalized patients. According to a recently published study, psychiatric medications can account for up to 50% of the ADRs for hospitalized patients with mental illness, many of which can be attributed to drug-drug interactions.[1] ADRs resulting from drug-drug interactions leading to hospitalization are often preventable. It has been estimated that 26% of ADRs requiring hospital admissions may be due to drug-drug interactions.[2]

Even ADRs that are deemed to be "not severe" can have significant impact on patients with a psychiatric illness, as a growing body of evidence suggests a strong relationship between drug-drug interactions, treatment failures, and higher health care costs due to avoidable medical complications.[3] While only a few of the possible drug interactions may be clinically relevant, the practitioner still must consider critical factors associated with drug-drug interactions. Such factors include the potency and concentration of the drugs involved, the therapeutic index balanced between efficacy and toxicity, the presence of active metabolites, and the extent of the metabolism of the substrate drug.[4]