Final answer:
The exaggerated side effects such as rapid heartbeat and excessive perspiration from medication is most likely due to heightened activity in the sympathetic division of the autonomic nervous system.
Step-by-step explanation:
The side effects, like rapid heartbeat and excessive perspiration, experienced by your brother due to the prescription medicine are likely because the medicine is exaggerating activity in the C) Nervous system.
More specifically, these effects are consistent with increased activity in the sympathetic division of the autonomic nervous system. This division is responsible for the 'fight or flight' response, which elevates the heart rate, increases respiratory rate, and causes sweating among other physiological changes.
Medications that mimic the actions of adrenergic molecules, such as norepinephrine or epinephrine, can stimulate the sympathetic nervous system. In turn, this can lead to an increase in heart rate and perspiration, similar to what we might see with a natural stress response.