What term describes a medication's effect over time?

The term that describes a medication's effect over time is pharmacokinetics. This field studies how a drug is absorbed, distributed, metabolized, and excreted in the body, which collectively determines the concentration of the drug in the bloodstream at any given moment. Understanding pharmacokinetics is essential for optimizing medication regimens, as it informs how often a drug needs to be administered and in what dosage to achieve the desired therapeutic effect while minimizing side effects.

Pharmacokinetics is distinct from other terms in the options. For instance, synergy refers to the interaction between two or more substances, where their combined effect is greater than the sum of their individual effects—a concept relevant for drug interactions but not specifically time-related. Efficacy indicates how well a drug produces its desired effect at a certain dose but does not describe the time factor of these effects. Bioavailability specifically relates to the proportion of a drug that enters circulation when introduced into the body and is available for action, rather than how that action unfolds over time. Thus, pharmacokinetics is the most appropriate term in this context.