Pretty much all absinthe is made with the herb Wormwood (incidentally, Wormwood was an ingredient of Vermouth originally, and from a corruption of the word "wormwood" we get "vermouth").
The thing you're interested in is the psychoactive ingredient of wormwood - Thujone.
It has been disproven that any absinthe - modern or historical - has had any thujone content whatsoever.
There was a fascinating article about a biochemical scientist whose life work was absinthe published in Wired magazine. Check it out here -
http://www.wired.com/wired/archive/13.11/absinthe.html