"When you take drugs, the drug goes through your bloodstream, and later on in your life that drug can come back up into a flahback when you have used the drug. You could have taken LSD one day, and a year down the road it can come back into effect and you can start hallucinating again. And it's not just LSD, it's every drug."

http://no.drugfreeworld.org/#/docume...umentary-intro