Module 2: Basic Pharmacology of Controlled Drugs and Substances

Lesson 5

Genetic influences

As discussed in the first lesson, pharmacogenomics is the branch of science that identifies the genetic attributes of an individual that lead to variable responses to drugs (Malhotra, 2016). For example, genetic polymorphisms of the CYP2D6 enzyme (roughly 10% of the population) can alter the effect that codeine has on patients causing them to experience no analgesic effects of the drug at normal therapeutic levels: codeine must be converted to morphine-6-glucaronide in the cytochrome P450 pathway to be used as analgesia. There is also variable enhanced conversion (in up to 40% in some ethnic populations) that has been associated with adverse events particularly in breast fed infants where mothers were given codeine (Guidelines for maternal codeine use during breastfeeding, 2009). Knowledge of patterns of genetic variation is necessary to design optimal treatment plans for individual patients. Given that this is a new branch of study, clinicians are encouraged to read about the topic of pharmacogenomics in a current pathophysiology or advanced practice pharmacology text.


  • Malhotra, A. (2016). An introduction to pharmacogenomics. In T. Moser Woo & M. Robinson (Eds.), Pharmacotherapeutics for Advance Practice Nurse Prescribers. Philadelphia, PA: F.A. Davis.