It’s not just the gun that’s smoking in American Ultra.

Directed by Nima Nourizadeh (“Project X”), “American Ultra” is a gleefully gory action comedy about a small town stoner who, unbeknownst to him, is a highly trained CIA operative.

Mike (Jesse Eisenberg) spends his time getting high and doodling a comic about a monkey astronaut but when a customer utters a strange sequence of words to him, Mike’s hitherto suppressed CIA training is activated. The agency targets him for termination and Mike’s plans to propose to his girlfriend are derailed when an army of assassins descends on the supermarket where he works.

Pitched as a weaponised “Clerks”, as it unfolds and reveals the degree to which the people around Mike were in on his little secret, it ends up being more of a militarised “Truman Show” that owes a great deal to the Bourne movies. The Bong Identity, perhaps?

It clips along at a fair old pace and there’s no shortage of invention and black humour in the many fight scenes and Mike’s tendency to use whatever’s lying around to dispatch his enemies. In assembling Jesse Eisenberg, Kristen Stewart and Topher Grace, the film creates the perfect trinity of unlikeable actors in the main roles and it almost unbalances the film, but the sparky script and conveyor belt of action keeps it ticking over. Like its central character, the movie can’t quite decide what it wants to be and gets distracted by flipping back and forth between action spy caper and stoner comedy.

Not quite as clever as it thinks it is, nor as sharp and satirical as you want it to be, “American Ultra” gets close to greatness but can’t quite make that final leap. Its disappointingly brief stay in cinemas on both sides of the Atlantic means we’re unlikely to see the promise of the amusing coda fulfilled in any sequels but if you’re looking for undemanding fun for 90 mins, “American Ultra” should do you nicely.