Which of the following is a side effect commonly associated with phenytoin?

• A. Rash
• B. Drowsiness
• C. Nystagmus
• D. Suicidal Ideation

Answer: (D)

Suicidal ideation is a recognized risk with all antiepileptic drugs, including phenytoin. Regulatory safety data include a boxed warning that AEDs can increase the risk of suicidal thoughts or behaviors, so clinicians monitor mood changes and suicidality when starting or adjusting phenytoin. While phenytoin has other common effects like nystagmus, rash, or drowsiness, the safety warning about suicidality makes this option the best choice to reflect a significant, monitored risk associated with phenytoin. If symptoms arise, prompt assessment and appropriate action are warranted.