How Can Drugs That Have Been Shown to Increase Alertness

How can drugs that have been shown to increase alertness and a sense of well-being as well as reduce physical and emotional pain also be dangerous?

A) They can disrupt the brain's neural pathways, thereby altering the chemical balances to produce dangerous behaviors or hallucinatory effects.
B) They can reduce the production of cerebrospinal fluid such that the CNS does not receive enough nutrients and hormones.
C) They can interrupt normal functioning of the optic nerve such that action potentials cannot reach the brain.
D) They can weaken the endoskeleton of the human body such that internal organs are not fully protected.