Starring Lou Taylor Pucci, Tilda Swinton, Vincent D'Onofrio, and Keanu Reeves. Rated 14A. Opens Friday, October 7, at the Fifth Avenue Cinemas

Lank-haired, sensitive teens have a hard time of it no matter what their circumstances. There's probably a law about it. But the problems of one such suburban lad, called Justin Cobb (Lou Taylor Pucci), are certainly amplified by his transparently Freudian habit of sucking his thumb.

Justin's underachieving nature is of ongoing concern to his mother (Tilda Swinton), who seems to want him as a flirtatious buddy more than a son, and to his stoically macho dad (Vincent D'Onofrio), who is still nursing defeat from a college football injury. There's a little brother (Chase Offerle), too, but he mostly stays out of the way.

In the Cobbs' nondescript little borough (unnamed, but actually various towns near Portland, Oregon), Justin isn't exactly the bottom of the geek pile, but he's currently on a slow train to Loserville. One bright spot is a sympathetic eye from Rebecca (Kelli Garner), smart beauty of the debate club run by a sharp-tongued teacher played by Vince Vaughn. ("This isn't the 'agree club'," he says after catching Justin fawning over Rebecca.)

The lad also gets frequent words of wisdom from his orthodontist, with whom he has spent many years, thanks to his digital fixation. Of course, when your orthodontist is played by Keanu Reeves, in enjoyably self-spoofing mode, you can expect that wisdom to be slightly out of whack. Like, how is finding his own "power animal" going to help him keep that damn thumb out of his mouth?

The school nurse has other ideas, and as fast as you can say, "Ask your doctor about possible side effects", Justin finds the chemical balance he didn't know he'd been looking for. Meanwhile, Mom, night nurse at a rehab clinic, is working through her own obsession with a TV hunk (played by Benjamin Bratt) whom she encounters when he goes into detox.

Everybody's sucking on something in this well-crafted tale from writer-director Mike Mills, a video maker here working from a novel by Walter Kim. (The rock soundtrack, from Polyphonic Spree, is as cool as you might expect.) As in Junebug and other Sundance-type dramas currently circulating at the lower reaches of the multiplex, character is far more important than conflict, and Mills is superb at drawing low-key realism from his well-matched cast, with Reeves and Vaughn providing needed boosts of energy to keep the thing going. (And when's the last time anyone said that about our Keanu?)

Bratt's cameo is far more problematic, because he is given a single scene in which to dazzle the viewer, provide some crucial back story, and resolve emotional issues between Justin and his mother. That's too much weight to bear, and it reveals the limits of the movie-or at least the desire of the filmmaker to go tidy where a little more mess would have been better. On the other hand, Thumbsucker heads toward an ending that looks artificial on paper but is genuinely uplifting in the experience. Like any teenager with real potential and unusual quirks, the movie ultimately earns its right to make mistakes and just keep going.