Lysergic Acid Diethylamide

LSD is the most powerful psychedelic drug on the planet.

W. Owen: Salvia divinorum (or more accurately, its active principal salvinorin A) is the most potent psychedelic compound known, at least in its pure form anyway.

Late Correction: actually I'm wrong. By weight, salvinorin A is still the most potent naturally occurring psychedelic compound, but LSD (semi-synthetic) still edges it out by a few micrograms.

That'll teach me to not hit the books before posting this shit.