Lysergic acid diethylamide, simply known as LSD because it's name is somewhat of a tongue twister, is an extremely controversial yet powerful hallucinogen.
The reason for LSD's controversy is because many of the users of the drug insist that the drug has aided them in becoming a better person, and that they've been able to do things that they couldn't do while sober.
Two examples of this are Nobel Prize Winners Kary Mullis, who discovered how to amplify certain DNA sequences so that we can view them.
The second example is the case of Francis Crick, the man who discovered the double helix structure that DNA is formed in.
That's right - the guy who came up with the double helix shape you studied in grade school, was tripping on acid.
However, the drug is such a strong hallucinogen, and many feel that the drug is unsafe because many people have died after believing their hallucinations to be real.
For example, the classic 'I'm flying' hallucination found in cartoons where the user thinks they've gained the ability to fly, and they jump off something very high...only to find that they can't actually fly.