enzyme inhibition
the ability of drugs or other substances to impair or arrest the ability of enzymes, especially liver (hepatic) enzymes, to metabolize those drugs or other substances. The cytochrome P450 enzymes that are responsible for the metabolism of numerous psychotropic drugs are susceptible to inhibition by psychotropics or other substances. Many of the SSRIs (selective serotonin reuptake inhibitors) inhibit the activity of enzymes for which they are substrates, leading to increased concentrations of the SSRIs or other drugs that are metabolized by the same enzyme. Enyzme inhibition can be competitive, when a drug partially inhibits an enzyme by competing for the same binding site as the substrate (the compound on which the enzyme acts), or irreversible, when a drug binds so completely to an enzyme that it fundamentally alters the enzyme and even partial metabolism of other substances cannot take place.