According to an article in Mixmag in 1999, the drug gurning etc was for real as the cast did have ecstasy and drank a lot of alcohol whilst filming.
'Pablo Hassan', the owner of Asylum (the nightclub they visit) is played by well known international DJ Carl Cox.
When Jip first picks up Koop in his car you hear the radio broadcast BBC's Radio One. The MC is Pete Tong, who is the movie's Music Supervisor. Pete Tong actually did have a weekly radio show on Radio One.
The 'Making of' feature on the Remixed DVD goes into the difficulties of filming a 4 minute Steadicam tracking shot. This shot never appeared in the final version of the film and led to the first Assistant Director leaving the project.
There is another cut of film called Human Traffic Remixed. According to The Guardian there were rumors that Justin Kerrigan wasn't involved with edited version but the producer Allan Niblo was. There are also rumors that they had fallen out during the shoot. It is available on DVD in the UK