You are answering a USMLE-style medical question. Question: A 5-year-old girl is brought to her pediatrician for evaluation of difficulties noted at school. Her kindergarten teacher voiced her concern that the child ‘spaces out’ often and thinks she may have ADHD. The parents deny any history of head trauma or infection. Her blood pressure is 106/74 mm Hg, the heart rate is 69/min, and the respiratory rate is 14/min. Physical exam demonstrates a happy child who has reached developmental milestones. Laboratory results are within normal limits. EEG demonstrates a 3-Hz spike and wave pattern (see image). The decision is made to start the child on medical therapy. What should be advised to the parents as a potential side effect of the first-line medication? Options: A) Nystagmus B) GI upset C) Facial rash and blood in the urine D) Weight gain and change in hair color Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.