The Collaborative International Dictionary of English v.0.48:

hallucinogen \hal*lu"ci*no*gen\ n.
   A substance capable of producing hallucinations when
   ingested; a hallucinogenic substance; as, LSD is a powerful
   hallucinogen.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

hallucinogen
    n 1: a psychoactive drug that induces hallucinations or altered
         sensory experiences [syn: hallucinogen, hallucinogenic
         drug, psychedelic drug, psychodelic drug]