When someone on a trip starts to wig out, you take them someplace quiet and talk soothingly and assure them that everything's going to be OK. But as the tagline of this film makes clear, for these characters everything is most definitely NOT going to be OK.
For those who haven't read the book, it's important to know what you're getting into. PK Dick wrote this novel as a way of telling the story of how he and his friends in the early '70s damaged and destroyed themselves with drugs. He tells this story within the framework of a surreal science fiction thriller, but many of the scenes are straight from his own experiences with the unpleasant consequences of people using drugs and disintegrating mentally.
This film does an amazing job of capturing the feel and tone of the book as well as the paranoia, perceptual distortions, and chaos of hallucinogenic overindulgence. Add to that a story that only gradually emerges from the madness, but by the end brings in a lot of heavy ideas such as the existence of free will, whether ends justify means, etc. There is a sense of consequence to what happens in the film, a sense of despair at what has been lost. So this story of drug-addled losers becomes the story of the human struggle for identity and meaning.
I have a couple of minor quibbles regarding scenes from the book that only partially made the cut (no explanation for the significance of "If I'd known it was harmless I would have killed it myself, no little kid to explain how 6 and 3 gears means 18 speeds). Still, most adaptations of PK Dick stories take a few basic ideas and try to shape them into more conventional films that fit into established genres. Even when it works, such as with Blade Runner or Total Recall, it's not really PK Dick. Not so this film. This is PK in all his dark and perverse and deeply thoughtful glory.