It's always interesting when a small molecule (ingested as a pill) has a dramatic effect on human behavior. Clearly, the molecule itself can have no effect on us unless it exploits something which already exists in the brain.
For example, ingesting the psilocybin molecule (found in some mushrooms) switches production of one of the brain's neurotransmitters (serotonin) into overdrive. If your brain produces too little serotonin, you're depressed. A little more serotonin, and you feel excited. But if the brain produces a lot of serotonin, you'll have a mystical "feeling of sacredness or awe, and deeply felt positive mood like joy, peace and love".
There's nothing abnormal about this. The brain is designed to behave normally with varying levels of serotonin, as an automobile is designed to drive normally at slow, medium or high speeds. The fact that the brain leaves itself open to be exploited by an ingested chemical (like psilocybin), shows that the brain is waiting for signals, for which it is designed to respond. A slight change to the psilocybin molecule's form itself, and the brain would simply ignore it.
But the psilocybin molecule can make us excited when there is no event. We simply ingest the pill, and feel that something very important and transcendent took place. We may even end up a permanently changed person, more "compassionate, loving, optimistic and patient".
The point is -- the brain has this complex response built-in already. Psilocybin doesn't cause it; it evokes it.