In a world where an authoritarian, out-of-control government snoops and pries into your every move, ostensibly in search of criminals/terrorists/evildoers, paranoia seems less like a mental disorder and more like a rational response to the situation.

This is one of the perhaps unintended messages of A Scanner Darkly, the Richard Linklater adaptation of the Philip K. Dick novel that opened July 7. Linklater effectively combines the anti-drug and anti-government surveillance themes of Dick’s prescient novel (which I admit I haven’t read) for this thought-provoking if not always gripping film version.

The medium is the message for Linklater, who uses rotoscoping — shooting his live actors on digital video and then “animating” them so that they are recognizably Keanu Reeves, Robert Downey Jr., Winona Ryder, Woody Harrelson et. al., and yet not. It’s an ingenious way to create a feeling that this near-future dystopia is both unreal and realer than real, even if the novelty wears thin just as the plot starts to thicken.

One of the most effective uses of rotoscoping is its ability to show an identity-masking suit that narcotics agent Fred (Reeves) wears when he reports in to his superior “Hank” in the Orange County, California police department. The suits are necessary for both parties because the government’s surveillance technology has become so adept at finding and identifying anyone, anywhere, any time — even (especially?) the narcs. They protect the wearer’s identity by projecting a constantly morphing blend of physical traits — all ages, races, features and genders, shifting like an ever-spinning kaleidoscope. It’s an off-putting effect at first, as it’s meant to be, but it’s used to good effect as the Reeves character begins to crack up, and sees ever-more-freakish faces on himself and others.

These and other visual touches (license plates no longer have letters and numbers, just bar codes, so you need a scanner to read them and they are presumably harder to fake) do as much to create the paranoid world the characters inhabit as the dialogue and action. The problem is that the characters Dick and Linklater use to tell the story are less interesting than their milieu.

In Scanner, addiction to the drug “Substance D” has become a major health crisis. Substance D combines the worst elements of a number of legal and illegal pharmaceuticals, with the addictive power of nicotine and crack cocaine, the paranoia of marijuana, the hallucinations of LSD and the identity loss of heroin. Most pernicious of all, D users never realize they’re overdosing; several times during the film, one character asks another “How much do you take?” There’s always a delicious, scary pause before the user replies “Not that much.”

The only “cure” for Substance D addiction is rehab at clinics run by New Path, a corporation that’s won the exclusive contract to dry out the heavy-duty D freaks (hmmm, contractors hired to do the government’s dirty work with little or no accountability or oversight — that could never happen in the real world).

Reeves, who does fine, understated work in Scanner, has a dual identity — both narcotics agent Fred and Bob Arctor, his cover as he portrays a D user who is trying to move up the pharmaceutical food chain. Unfortunately the D is disconnecting the two hemispheres of his brain, so Fred doesn’t always know that he’s Arctor, and Arctor doesn’t always seem to know he’s under surveillance. Fred has a wife and two daughters, seen in flashback, who may or may not be real. Ryder is Donna Hawthorne, a small-time dealer and Arctor’s girlfriend (though she refuses to sleep with him — one effect of persistent D use is a shrinking of the libido).

Rounding out this rogue’s gallery are Charles Freck (Rory Cochrane), Ernie Luckman (Woody Harrelson) and James Barris (Robert Downey Jr., who presumably knows whereof he speaks when playing a paranoid drug addict/informer/illegal chemistry genius). Downey ’s ability to sound reasonable even as he’s spouting utter nonsense, and Harrelson’s combination of good ’ ol boy aggression and surfer-boy stupidity, are both amusing for a while; Cochrane’s twitchy, hallucinating nutjob is less so.

With the exception of the identity-masking suits, Linklater, who also wrote the script, keeps the animation tricks to a minimum. This is a smart but tough decision, because once we get used to the rotoscoping, Scanner’s story plays out almost like a live action film. However, it’s a live action film with a draggy middle section, with the Reeves character(s) going all philosophical on us during a sex scene. By the time we get to the conspiracies within conspiracies that have been fueling the plot, the political side of my brain was satisfied, but my dramatic side had the munchies.

Sci-fi and Philip K. Dick fans, as well as anyone interested in the variations of animation that are making this an exciting time for filmmakers, should see Scanner. Needless to say, conspiracy theorists will see their worst fears justified by it. As for the rest of you/us, A Scanner Darkly may be more to be admired than enjoyed