T2 Trainspotting Ewan McGregor, Jonny Lee Miller, Robert Carlyle. Directed by Danny Boyle. Rated R. Opens Friday at Downtown Summerlin.

Early in T2 Trainspotting—a belated, rather clumsily titled sequel to Danny Boyle’s 1996 film (adapted from Irvine Welsh’s novel) about Edinburgh heroin addicts—the movie’s central figure, Mark Renton (Ewan McGregor), visits his childhood bedroom and puts a record on his old turntable. We hear literally less than a second of the opening drumbeat to Iggy Pop’s “Lust for Life” before Renton lifts the needle. That song memorably accompanied Trainspotting’s frantic opening sequence, as Renton, then 26 years old, ran through the streets following a shoplifting spree, with security guards in hot pursuit; now, at age 46, he can’t bear to listen to it. Trainspotting depicted what it was like to be a young, heedless junkie. T2, though based in part on Welsh’s 2002 follow-up novel, Porno, is fundamentally a portrait of middle-aged regret, throwing in constant visual references to the first movie by way of emphasizing how little has changed.

Indeed, if you’ve never seen Trainspotting—or even just haven’t seen it for many years—watching (or rewatching) it in preparation would be a good idea, as T2 assumes pretty strong familiarity. One needs to know, for example, that Renton stole a lot of money from his pals at the end of the first film, as the easily enraged Begbie (Robert Carlyle), who’s in prison as the sequel begins, has not forgiven that betrayal. Neither, for that matter, has Sick Boy (Jonny Lee Miller), now known as Simon, though that doesn’t stop him from enlisting Renton in a plan to convert an old pub into a brothel. The other surviving member of the group, Spud (Ewen Bremner), is still hooked on heroin, but gradually discovers, over the course of the movie, a hitherto untapped talent for writing, fashioning stories from the adventures seen in Trainspotting.

T2 works best at its most cheekily self-referential. The very first shot, for example, is a facsimile of the original’s opening shot, with Renton’s feet suddenly landing in the frame and running forward … except this time it turns out that he’s on a treadmill at the gym. The famous “Choose life” speech gets a 21st-century update later on, and Boyle, returning as director, repeatedly splices in moments from the original that serve as stark reminders of the toll that time has taken. (Even in the midst of their self-generated squalor, they all look brand-new.) But the movie—which is 20 minutes longer than its fleet predecessor—loses its way in the second half, focusing too much on Begbie’s quest for revenge and on Veronika (Anjela Nedyalkova), a Bulgarian sex worker who wasn’t in the first film at all and feels out of place here. “Lust for Life” eventually gets played, but it’s a new remix, and it’s just not quite the same. Nothing ever is.