Coming on like 'Geekz n the Hood', Dope follows a trio of self-confessed nerds as they nervously negotiate their dicey Inglewood neighbourhood – known as 'the Bottoms' – and try to stay out of trouble. Writer-director Rick Famuyiwa's fifth film sets itself apart from gritty urban dramas with its non-conformist leads, bounce and cheerful aesthetic that skilfully fuses the retro and contemporary. But it falls into another trap as it descends into a farcical adventure.

Malcolm (Shameik Moore) and pals Jib and Diggy (Tony Revolori and Kiersey Clemons) are about to graduate high school, where they've been regular targets for bullies due to their academic inclination, dated threads, and fondness for 90s hip-hop and 'white shit'. The teens wangle their way into a local tough's birthday party where Malcolm pursues his wafty dream-girl Nakia (Zoë Kravitz) but, when events are interrupted by a shoot-out, they're drawn into the world of drugs and guns.

From here on in it frames these interesting characters within a crude crime caper narrative, which might hope to emulate films like Pulp Fiction, After Hours and Go but that judders along, frequently failing to convince. Though our heroes' whole futures are on the line there's little sense of jeopardy, the trio's careful avoidance of the criminal path is surrendered too blithely, and the cartoony presentation of gangbangers and drug-addled seductresses is at odds with the film's initial sensitivity and subversion.

Nevertheless, Dope is lively, positive and likeable, with a protagonist who resists easy definition and plenty of visual pop. And it's further energised by a propulsive, evocative soundtrack (including classics from Public Enemy, Nas, A Tribe Called Quest and four original songs written by Pharrell Williams). Yet any truthfulness struggles to survive the contrivances and Moore's nuanced performance feels suffocated by the sheer flipness of it all, while Revolori (The Grand Budapest Hotel) and Clemons are deprived of back-story and depth.

There's a serious point here about what it takes to get out of the ghetto – one that's well worth making – but it's messily and then preachily imparted; that Famuyiwa has to lay out this message in the form of a concluding speech suggests that he knows his film hasn't fully done its job.

Screening on Thu 25 and Fri 26 Jun as part of the Edinburgh International Film Festival 2015. General release from Fri 4 Sep.