1. Kelly Macdonald (recently the voice of Merida in Brave) got the part of Diane after responding to a "little yellow flyer" handed out by the production crew in Glasgow. She was working in a restaurant and hadn't acted before.
2. Although she played a 14-year-old in the movie, she was actually 19.
3. The producers had to cut several seconds from Macdonald's sex scene with Ewan McGregor for the US release because Diane "seemed to be enjoying herself too much". They were worried that would scandalise viewers in the States.
4. The other issue with the US release was the cast's strong Scottish accents. They ended up having to re-record the first 20 minutes of dialogue with "softer" accents.
5. Kelly Macdonald almost screwed up her first day of filming by getting drunk. It was a whole day and night shoot and she ended up in the pub for hours, so she had a hangover when she made her acting debut.
6. She also "naively" invited her mum and brother on to the set on the exact day the sex scene was being filmed. She made them hide in a catering van so they wouldn't see anything.
7. Trainspotting author Irvine Welsh initially wasn't too sure about adapting the novel into a film.
8. Director Danny Boyle managed to convince him by writing a letter stating that the proposed writer and producer, John Hodge and Andrew Macdonald, were “the two most important Scotsmen since Kenny Dalglish and Alex Ferguson”.
9. Irvine Welsh ended up having a cameo in the film: He plays Mikey Forrester, the drug dealer who gives Renton those fateful opium suppositories.
10. Before he took up screenwriting, John Hodge was a junior doctor who dealt with heroin addicts and he worked some of his experiences into the script, like the junkies stealing a television set from an old folk's home.
11. Ewan McGregor was first choice for the role of Renton before the film even went into production because of his stand-out performance in Danny Boyle's previous film, the 1994 Edinburgh-based dark comedy Shallow Grave, also written by John Hodge.
12. According to Boyle, for Renton they wanted somebody who had the quality "Michael Caine's got in Alfie and Malcolm McDowell's got in A Clockwork Orange" – a repulsive character with charm, in other words.
13. McGregor lost 2 stone to prepare for the role, and also shaved his head. He lost the weight by cutting out alcohol and dairy products.
14. He also read books about crack and heroin to prepare, as well as meeting recovering addicts from the Calton Athletic Recovery Group in Glasgow...
15. ...who taught him how to cook up heroin with a spoon using glucose powder.
16. McGregor even considered injecting himself with heroin in order to "better understand the character", but eventually decided against it.
17. For the scenes in the movie where Renton injects himself with heroin, the makeup team built a prosthetic arm complete with small pockets of fake blood that would burst when the skin was punctured by a needle.
18. The producers didn't want to "condone" drug-taking, but they did want to make sure that they portrayed it realistically.
19. The scene where Renton sinks into the floor after overdosing on heroin was achieved by building a platform above a trapdoor and slowly lowering McGregor.
20. The Calton Athletic drug addiction counsellors make an appearance in the film: They're the football team you see at the beginning.
21. Robert Carlyle has said that he played Begbie as a closeted gay man whose outbursts of violence were due to his "fear of being outed".
22. Irvine Welsh confirmed that he intended Begbie to have an ambiguous sexuality when he wrote the novel, and agreed with Carlyle's interpretation.
23. Carlyle doesn't enjoy watching himself on film. According to Kelly Macdonald, during the test screening he "was almost crawling on the floor with embarrassment. Every time he came on screen he would dip lower in his seat."
24. Danny Boyle’s first choice to play Begbie was future Doctor Who Christopher Eccleston, as he resembled the character as described in the book.
25. It looks entirely rank, but the shit in the "Worst Toilet in Scotland scene" was actually made from chocolate mousse and reportedly "smelled quite pleasant."
26. The whole film was shot in just seven and a half weeks and had a budget of £1.5 million.
27. Instead of having fancy trailers and catering, the cast and crew had to work out of an abandoned cigarette factory in Glasgow.
28. Despite the fact the film is set in Edinburgh, most interiors and exteriors were shot in Glasgow to save money (but not the chase down Princes Street, obviously).
29. The iconic "choose life" monologue was originally planned for the middle of the film, but Boyle and Hodge were struggling to find a suitable intro so they moved it to the beginning.
30. The famous opening sequence of the film (where Renton runs down Princes Street in Edinburgh) was inspired by the Spike Jonze–directed music video for "Sabotage" by the Beastie Boys.
31. Writer John Hodge took time off from writing A Life Less Ordinary to play one of the John Menzies security guards who chases Renton and Spud down the street.
32. It's also a nod to The Clash's video for "Bankrobber" in which the bank robbers in the video are being chased in a similar fashion and similar camera shot.
33. Danny Boyle knew a lot of the musicians whose work features on the Trainspotting soundtrack, like Primal Scream and Iggy Pop.
34. Irvine Welsh told Vice: "That helped us get the rights for a low cost, sometimes no cost. There's no way we'd have been able to get such a soundtrack normally."
35. The cast earned only about £700 a week, according to Danny Boyle.
36. Ewan McGregor worked incredibly hard, and only had one day off during the entire seven-week shoot.
37. Due to the low £1.5 million budget, most scenes had to be shot in just one take.
38. One exception to this was the scene where Renton is hit by a car. It took two hours and 20 takes to film, and McGregor was repeatedly attended to by the on-set nurse.
39. The film's distributor PolyGram was a bit less stingy with its budget, and allocated £800,000 to go towards promotion and advertisement, one of the biggest marketing budgets in history at that time.
40. It definitely paid off, as the low-budget film went on to make £48 million ($71 million) at box offices worldwide.
41. Jonny Lee Miller was the only non-Scottish main cast member. He got the part of Sick Boy on the strength of his performance in Hackers and his ability to do a great Sean Connery accent.
42. Coincidentally, his character in the film is obsessed with James Bond trivia.
43. The sequel to Trainspotting is currently being filmed on location in Scotland. It's loosely based on Welsh's follow-up novel, Porno.
44. Its working title is T2: Trainspotting 2, it's set 20 years after the events of Trainspotting, and it will feature most of the same characters and actors, including Ewan McGregor, Jonny Lee Miller, Ewen Bremner, and Robert Carlyle.
45. The title of the book and film do actually refer to the slightly obsessive hobby of waiting for trains and then writing their numbers down in a little book.
46. Irvine Welsh explained that, much like heroin addiction, trainspotting "is something that only the people who indulge in that pastime truly understand. To them, it makes perfect sense."