In 1997, Charlie Kaufman wrote a screenplay adaptation of A Scanner Darkly that was never produced. You can read it here.
Surprisingly, Kaufman’s version follows Philip K. Dick’s novel as closely as Linklater’s does, with few of the Kaufmanesque digressions that anyone who seen Adaptation might expect. Kaufman’s version has more profanity, and more references to the taking of real drugs (as opposed to the fictional Substance D). Where Linklater focuses on the interaction between Bob Arctor (Keanu Reeves) and the stoners he lives with (Woody Harrelson, Robert Downey, Jr.), Kaufman seems more interested in the dysfunctional relationship of Arctor and his “don’t-touch-me” dealer girlfriend (Winona Ryder). Thus, the scene in which the stoners bicker, as only stoners can, over how many gears it takes to make an 18-speed bicycle – a highlight of Linklater’s film – is not included in Kaufman’s scenario.
Again, I’m glad it was Linklater’s version that finally made it to the screen.