[Maniax]

You need to drink a lot of the real wormwood stuff (not legal in the US) in order to have hallucinations.  And by a lot, I mean you need to be a committed absintholic.   Not fun, from what I hear.  I rather like the taste of the stuff when properly mixed with sugar though.  I'd call it licorice-like.

[watsisname]

I keep hearing conflicting statements about the alleged hallucinogenic properties of absinthe and/or wormwood, and their legality, so I did some searching to see if I could find something concrete.

About absinthe:
Quote from http://www.wormwoodsociety.org/index.php?

Is Absinthe A Drug?  Is It Poisonous?  Is it Dangerous?

No, no and no. Contrary to popular misconception, absinthe is not hallucinogenic, psychedelic, or narcotic.  If you're looking for this kind of experience you'll be very disappointed in genuine absinthe.

Is Absinthe legal in the United States?

Yes, conditionally.

While there is no law that prohibits absinthe by name, any drink that contains in excess of 10ppm of thujone is prohibited from being imported into, or produced for sale and consumption in, the United States.  This is the same as the European Union limit for products labeal as absinthe.

NOTE: No regulations have changed.  Prior to May 2007 it was not widely known that the tolerance for official method of thujone analysis—10ppm—is such that it effectively legalizes many European absinthes.  This was a major breakthrough.  It also means that a number of pre-ban era absinthes would be legal in the US by modern standards, including the definitive premium absinthe brand, Pernod Fils.

Most of the laws that impact absinthe in the US are out-dated, convoluted, un-evenly enforced and misunderstood, even by those charged with enforcing them.

Due to recent changes in the understanding of these regulatory issues, genuine absinthe is once again reappearing legally in the US market.

Thujone:
http://en.wikipedia.org/wiki/Thujone

Thujone is a ketone and a monoterpene that exists in two stereoisomeric forms: (+)-3-thujone or α-thujone and (−)-3-thujone or β-thujone. It has a menthol odor. Even though it is best known for being a chemical in absinthe, recent tests show absinthe contains only small quantities of thujone, and may or may not be responsible for absinthe's reported psychedelic effects.

http://recipes.howstuffworks.com/absinthe.htm
This site also says thujone is present in wormwood, but specifically is simply a toxin, and only in very large amounts (you'd die of alcohol poisoning before being effected by the thujone).

Wormwood:
http://en.wikipedia.org/wiki/Absinth_Wormwood

[Flipside]

It's not the Absinthe on its own that is hallucinogenic, it's the reaction it has when it is mixed with other ingredients, particularly alcohol, which is in and of itself a mild hallucinogen. Kind of like the fact that Beer and Cider are both moderately strong drinks, but Snakebite, a mixture of the two, has a much more profound effect.