A 14-year-old boy is being treated for behavioral difficulties at home and at school and has been diagnosed with ADHD. He has been skipping class and often comes home smelling of cigarette smoke. His parents report he has developed sudden facial twitches and makes more frequent repetitive guttural sounds, especially since starting a new medication. His drug screen is negative for unprescribed substances of abuse. Which of the following is the most likely cause of his facial twitches and guttural sounds?

Choice A reason: Nicotine use may cause mild tremors or restlessness but does not cause the motor and vocal tics described. Choice B reason: Atomoxetine is a non-stimulant ADHD medication that rarely causes tics; its side effects are mainly gastrointestinal or related to sleep disturbance. Choice C reason: Guanfacine is often used to reduce tics, not provoke them, as it modulates noradrenergic activity. Choice D reason: Amphetamine, a stimulant, can exacerbate or induce motor and vocal tics, especially in individuals predisposed to tic disorders. The dopaminergic stimulation in the basal ganglia increases motor excitability, leading to repetitive movements or sounds resembling Tourette-like symptoms.