Twenty years ago, Trainspotting became a landmark film for a generation — a pitch-black comedy about hopelessness, addiction, friendship and the struggle to get life back on track, based on a novel by Irvine Welsh. (Click to see Tom Power's interview with Welsh.)

The movie's music also became a soundtrack for Gen X, and is still regularly named as one of the best film soundtracks of all time.

The sequel, T2 Trainspotting, opens in select theatres this weekend, and brings most of the troubled characters back together. Before we meet them, we thought it would be worth remembering some of the funniest, harshest and most unforgettable scenes from the original. (Warning: they contain strong language, violence and drug use.)

In the unforgettable opening sequence, we meet heroin addict Mark Renton (Ewan McGregor) and his quirky friends — con artist Sick Boy, kind-hearted and dim-witted fellow addict Spud, clean-cut athlete Tommy and violent psychopath Franco. "Choose life. Choose a job. Choose a career. Choose a family. Choose a f--king big television," says Renton in a voiceover, as his character sprints away from police, stolen goods tumbling out of his pockets. To boot, it's all set to Iggy Pop's propulsive "Lust For Life."

To the tune of the Lou Reed classic "Perfect Day," Renton takes a hit of heroin and shows what it's like — both for him and, much less romantically, for those around him.

We'll spare you the finer details, but Renton shifts his medication, which causes him to need a toilet — urgently. So urgently, in fact, that when faced with the worst toilet in all of Scotland, he doesn't continue his quest. The result is a hilariously horrifying — and for a few moments oddly beautiful — scene, set to Brian Eno's "Deep Blue Day." Guaranteed you'll never see a grungy public bathroom the same way again.

In the film's most brutal scene, the characters are awoken from their drugged haze by a woman screaming hysterically — only to discover that her baby has died. The likely father, Sick Boy, is devastated, and yells at his friends to say something. Only Renton breaks the silence: "I'm cooking up."

In a visually striking scene, Renton tries to kick his habit by getting locked into a bedroom at his parents' house, complete with kids' train-covered wallpaper. "Need like nothing I've ever know will soon take hold of me," he says. "It's on its way." As he goes into withdrawal, Renton experiences a series of creepy hallucinations, with Underworld's "Dark and Long" as a sonic backdrop.

Sick Boy came off heroin at the same time as Renton, though much more easily, then subjected Renton to his comical "unifying theory of life" — basically the idea that we are all in a steady state of decline. "At one point you've got it, and then you lose it and it's gone forever," Sick Boy says, pointing to pop-culture icons from Elvis Presley to David Niven, while also pointing a gun in a park. "All walks of life."

In the end, Renton makes his escape, and takes thousands of dollars in cash, knowing it will throw Franco into a violent rage. Spud watches him go and they share an unspoken goodbye. So why did he do it? "I could offer a million answers, all false. The truth is that I'm a bad person. But that's going to change. I'm going to change. This is the last of that sort of thing. I'm cleaning up and moving on. Going straight and choosing life," Renton says in a voiceover as he walks away to Underworld's club hit "Born Slippery." "I'm going to be just like you."

Watch the original Trainspotting trailer:

Watch the T2 Trainspotting trailer:

T2 Trainspotting is in select theatres starting this weekend.