Simon Posford (born 28 October 1971), better known by his stage name Hallucinogen, is an English electronic musician, specializing in psychedelic trance music. His first studio album, Twisted, released in 1995, is considered one of the most influential albums in the genre.

His second album, The Lone Deranger, was released in 1997. A third album consisting of Hallucinogen tracks remixed by the artist Ott, In Dub, was released in 2002.

He is also the founder of the label Twisted Records and works in the electronic groups Younger Brother and Shpongle. Younger Brother initially began as a side project of Posford and Benji Vaughan and represented a transition away from previous projects which emphasized a more synthesized style.

His grandfather, George Posford, was a composer and producer in the United Kingdom in the 1930s.