Phenytoin is an antiepileptic drug well-known for causing gingival hyperplasia as a side effect. This occurs due to the drug’s effect on fibroblast proliferation and extracellular matrix production in the gingival tissues. Clinically, this manifests as an overgrowth of the gums, which can lead to discomfort, difficulty in oral hygiene, and increased risk of periodontal disease. Patients on phenytoin require regular dental monitoring to manage this side effect effectively. Unlike warfarin or metformin, phenytoin’s impact on gingival tissues is direct and dose-dependent.

Reference: Harrison's Principles of Internal Medicine, Jameson et al., 20th Edition.