Rhys Ifans became firm friends with Howard Marks several years before the film was made, and extracted a promise that he would star if a movie of the dealer's life was ever produced.
That really is David Thewlis' penis that we get a glimpse of in a poolside scene. Originally his agent rang up and spoke to writer-director Bernard Rose, saying that he couldn't possibly reveal his penis as he was in the Harry Potter films! Thewlis however disagreed.
In development hell for over a decade.
There's been some criticism leveled at Chloë Sevigny for the quality of her English accent. In fact, Savigny rehearsed diligently to perfect the accent using tapes and voice coaches, but was somewhat thrown when Bernard Rose insisted on going off-script and improvising.