The cytochrome P450 (CYP) enzyme system is involved in the metabolism and elimination of numerous widely used drugs.

Inducers are molecules that increase activity. Enzyme induction is a process in which a drug induces (i.e., initiates or enhances) the expression of an enzyme.

An enzyme inhibitor is a molecule, which binds to enzymes and decreases their activity. Inhibitors are molecules that decrease enzyme activity. Inhibitors compete with other drugs for a particular enzyme thus affecting the optimal level of metabolism of the substrate drug which in many cases affect the individual's response to that particular medication, e.g. making it ineffective.

Isoforms are closely related variants of enzymes.

The material or substance (e.g., drug) on which an enzyme acts. To catalyze a reaction, an enzyme must be able to combine with its substrate.