A. Decrease in impulsivity: Atomoxetine is a selective norepinephrine reuptake inhibitor used in the management of ADHD. Its therapeutic effect is seen as improved attention span, reduced impulsivity, and better behavioral control. A decrease in impulsivity indicates improved executive functioning and is a direct marker of medication effectiveness in adolescents. B. Decrease in fasting blood glucose level: Atomoxetine does not have a primary effect on glucose metabolism. Changes in fasting blood glucose are not used to evaluate its therapeutic efficacy and would be unrelated to its mechanism of action on norepinephrine pathways in the central nervous system. C. Decrease in weight: Weight changes, particularly decreased appetite and potential weight loss, are recognized adverse effects of atomoxetine. While monitoring growth is important, weight reduction is not an indicator of therapeutic success and may instead require nutritional assessment. D. Decrease in blood pressure: Atomoxetine is more commonly associated with mild increases in blood pressure due to its sympathomimetic effects. A decrease in blood pressure is not expected and does not reflect improved ADHD symptom control, making it an unreliable indicator of effectiveness.