Why Is It Impossible to Predict Whether a User of Hallucinogens

Why is it impossible to predict whether a user of hallucinogens will have a "good trip" or a "bad trip"?

A) The drug effects depend very much on the user's expectations and past experiences with hallucinogens.
B) The hallucinogens as a class are very unpredictable and unstable in their effects on the human nervous system.
C) The hallucinogens have received virtually no clinical study in humans due to the heavy governmental restrictions on their use.
D) The physiological side effects of the hallucinogens are so dramatic that they make the "good" and "bad" effects difficult to sort out.