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The fun of “Side Effects” lies in figuring out what sort of movie it is even as you’re watching it. A sleekly clever murder mystery, the film plays as many games with the audience as it does with its characters, and for the majority of the running time — before the plot resolves into something smaller and meaner than you might have been expecting — the challenge comes from matching wits with what you’re seeing. Movies aren’t supposed to be this tricky anymore, are they?

They are when Steven Soderbergh is running the show. Working once more with screenwriter Scott Z. Burns (“Contagion,” “The Informant!”), the director sets up a dramatic situation whose suspense radiates out in many directions. There is a couple: Martin (Channing Tatum), who’s just out of jail after serving time for insider trading and wants his one-percenter’s lifestyle back, and Emily (Rooney Mara), the wife who wilted into depression after the feds showed up at their Connecticut mansion and who has since downsized into a Manhattan apartment, job, and funk.

There are also two psychiatrists: Dr. Victoria Siebert (Catherine Zeta-Jones), the poised shrink who treated Emily in Greenwich, Conn., and Dr. Jonathan Banks (Jude Law), an empathetic but dangerously overconfident specialist who takes on the patient after she rams her car into a parking garage wall. The opening half-hour of “Side Effects” takes us deep into Emily’s desolation, with Soderbergh’s camera mooring her in the frame like an abandoned dinghy. He plays games with the color palette and the sound mix; Mara has a spooky, translucent vulnerability that reminded me of Mia Farrow in “Rosemary’s Baby.” The actress gives a fully committed portrayal of someone who’s not all there.

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Soderbergh and Burns lay little traps here and there, and you start to get on edge wondering which ones will spring shut. Will “Side Effects” turn into a wellness melodrama? A conspiracy thriller? An anti-Big Pharma message movie? Or something else entirely? The screenplay is awash in borderline hilarious anti-depressant brand names, some real, others invented: Dr. Siebert recommends Ablixa, Dr. Banks has signed up (for a hefty paycheck) to participate in a trial for Delatrex. Emily’s boss offers her Cilexa, while the wife of Martin’s business colleague swears by Effexor. The camera occasionally moves in on a lone pill bottle silhouetted on a nightstand until it’s as big as the monolith in “2001.” Is this our villain?

Someone dies — sorry, I can’t say who — and not very nicely at that. At this point, “Side Effects” starts putting its cards on the table, very slowly, one by one, and experienced movie poker players will be able to spot the tell sooner or later. I can say that the death becomes a tabloid sensation thanks to the medication angle — Burns’s screenplay wickedly plays into our paranoid distrust of all the chemicals we gobble up — and that one of the doctors gets painted into a corner, with patients jumping ship, a spouse fleeing, and a license in danger of being revoked.

Who, exactly, is the main character here? That’s part of the puzzle. Mara’s Emily is the obvious choice, if only because Soderbergh’s camera adores her in all light and with all lenses. But the movie keeps forcing us to switch sides, shifting sympathies from the depressed wife to the struggling ex-con to the psychiatrists who may or may not have been lied to by one person or many, then back to the wife . . . When one of the four begins to put the pieces together, “Side Effects” looks like it’s settling decisively into a detective movie, but even that thrill is short-lived. The movie’s a pleasure to watch, but it has a very tasteful case of ADD.

And it comes to ground with a climactic twist that’s lurid and mildly kinky and surprisingly retrograde coming from this director. By the last few scenes, you realize “Side Effects” has been a genre exercise all along and that Soderbergh has had fun — maybe too much fun — convincing us he was going for something bigger. Then he seems to lose interest, and the film turns sour, even smug, with a final shift of sympathies that’s possibly unintended and certainly one too many.

Soderbergh has lately been making public noises that this will be his final film for a while, maybe ever, and, really, what else does he have to prove? He conquered Sundance with “Sex, Lies, and Videotape,” won an Oscar for “Traffic,” has done no-budget experimental (“Bubble,” “Schizopolis”), and mega-budget star vehicles (“Ocean’s Eleven” et al.). He has shown his proficiency with biopics, comedy, sci-fi, action, and more. His previous film, “Magic Mike,” was about male strippers, and it was as smart and enjoyable as anything he has done.

In “Side Effects,” he just messes with our heads — expertly, of course, but mostly because he can. This is what it looks like when a great filmmaker gets bored.