We've all taken drugs before. Even if we've never been aware of it...
When we go to sleep at night. Our brain's (or more specifically, the pineal gland) will produce a substance called DMT (Dimethyltryptamine).
DMT is a naturally occuring hallucinogen. This is the substance which causes us to have our wild dreams at night.
So when we are deep asleep and dreaming. We are actually, by definition -hallucinating.
The same thing applies when we ingest DMT (taken orally) you could hallucinate with your eyes open. Many people refer to this as the fourth dimension.
The ancient shamans of old times would concoct a brew called Ayahuasca which contained DMT and this would lead them to have visions and induce trance like states in which they would prophesize the future.
Interestingly enough, by ingesting DMT - you could hallucinate with your eyes open or closed (as opposed to sleeping - which is generally done with the eyes closed)
It is also believed that when we die, the brain produces DMT - so could this be the molecule that leads us onwards to the afterlife?