What is a side effect of phenytoin?

• A. Rash
• B. Weight gain
• C. Hair loss
• D. Hypertension

Answer: (A)

Rash is a recognized adverse effect of phenytoin because the drug can trigger a hypersensitivity reaction in the skin, ranging from mild rashes to more serious conditions like Stevens-Johnson syndrome. This makes rash the best answer since it is a well-documented, clinically important side effect that clinicians monitor for and often must stop the medication if it appears. Other options don’t fit phenytoin’s typical profile: weight gain and hypertension aren’t common direct effects of phenytoin, and phenytoin more often causes hair growth changes (hirsutism) rather than hair loss.