Which term best describes the drowsiness caused by Phenytoin?

The term that best describes the drowsiness caused by Phenytoin is a side effect. Side effects are unintended, secondary effects of a medication which can occur alongside the desired therapeutic effects. In this case, while Phenytoin is primarily used as an anticonvulsant to manage seizures, drowsiness is a common side effect experienced by some patients taking this medication.

Understanding side effects is important in pharmacology as they can influence patient compliance and overall treatment outcomes. Identifying such effects allows healthcare providers to better manage patient care and adjust treatment protocols as necessary. Adverse reactions are typically more severe or harmful and can lead to discontinuation or a change in therapy, while contraindications refer to specific situations or conditions that make a particular medication unsafe. Drug interactions involve one drug affecting the activity of another and do not directly relate to the inherent effects of a single medication on the body.