Eddie Jessup is a Harvard professor researching into the effects of hallucinogens on schizophrenia sufferers. After an experiment on himself involving a rare Mexican drug and an isolation tank, his body appears to partially regress into some pre-homo-sapien form. What is happening to him, and does he dare to continue with this work ?

Everybody should have at least one stoned-out movie they like. For most people it's Easy Rider or Head or The Cool And The Crazy, but for me it's the much more disturbing and visually dynamic Altered States. I think the reason for this is that the trippy effects in this film are terrific and an integral part of the plot, as opposed to just the usual psychedelic rubbish prevalent in some late sixties flicks. Russell's set-piece montages of disturbing horror and sexual/religious iconography are familiar from earlier movies like Tommy and Lisztomania, but the opticals and visual effects make-up by Brian Ferren, Dick Smith, Robert Blalack and Jamie Shourt are astonishingly eye-popping, rendered all the more unsettling by an ominous, growling score by John Corigliano. I guess Russell's style isn't to everybody's taste, but if you're willing to go with it I think he's one of the most visually and thematically exciting directors there has ever been (my favourite of his films is the goofy low-budget vampire flick The Lair Of The White Worm). All the more amazing in this movie is, despite the crazy story and the wild imagery, the whole thing works well as a drama of obsession and redemption. This is largely because of the fearless cast, who hurl themselves into character with terrific abandon. They're crazy people, but crucially they are believable crazy people. They yell at each other in complicated anthropological lingo about stellar conceptual notions, but in a way that brings the story to life, with many touching scenes, like the one where Hurt tells the story of his father's death, the genesis of his quest for truth amongst the infinite. All four leads are excellent (it was Hurt's first film), and Puerto Rican dancer Godreau gives a great physical performance as the simian alter-ego of Hurt's primal urges. Look fast for Drew Barrymore in her movie debut, aged five. Based on a book by Paddy Chayefsky (Marty, Network), who wrote the script but is billed here as Sidney Aaron (his real forenames) after falling out with Russell. This is a tremendous horror / science-fiction / drama which - whether you like it or not - you won't forget in a hurry. Movies are my drug of choice; they don't screw up your body but they can give you a terrific high and open up your mind, and this one is a terrific fix.

... and an early example of psychedelic horror.

I wanted desperately to like Altered States, because the things it gets right it gets so right. But sadly it's such a tonally inconsistent film, and one that can't seem to focus on anything at all. First it's about a Judeo-Christian concept of hell and the devil, and then it's about some ancient indigenous deity and spirituality, and then it's about some extra-dimensional being, and then it's about genetic memory and body horror, before finally referencing alternate universes. The tone of the film is also sadly inconsistent. At times it's closer to a romantic drama than anything else. When it actually gets down to the horror part it swings strangely between themes of the paranoid mad scientist and the grand tone and sweep of man vs God.

It's memorable for some of the great special effects of its time, but overall it feels like a conversation you have when you're 19, think you know everything, get really baked, and then start rambling about philosophy with your friends.