The drug, called NZT, is a black market test product that fate places in the hands of a blocked novelist named Eddie Morra (Bradley Cooper).
He swallows a pill and the effect is as seductive as it is transformative - Eddie finishes his dead-end novel in a few weeks, drops it on the desk of his astounded editor, then reels in the gorgeous girlfriend (Abbie Cornish) who dumped him when he was a washed-up loser.
As a power trip geared to young males, the movie's kick is as strong as anything in "The Social Network" with the bonus of glamorous Cooper in the lead. With "Limitless," he jumps to the front rank of male leads with a performance that combines camera-magnet good looks and the emotional/psychological acrobatics the role requires.
"Limitless" sets up as a classic Faustian bargain - Eddie's insatiable intellect makes him a master of arts, sciences, and (crucially) Wall Street finance, but it comes at a price.
Eddie learns that other NZT guinea pigs are dead, or walking zombies with burned-out brains. Moreover, as possessor of the world's only supply, he's the target of shadowy operatives and Russian mobsters.
How far can Eddie take things? At what cost?
These are questions that "Limitless" couches with smart, contemporary ideas. Director Neil Burger stages Eddie's transformation in front of a laptop, linking NZT to the sort of digital-age empowerment that turns a Zuckerberg into a Hearst overnight.
Morra also gets a job on Wall Street, mastering the quantitative algorithms that make him a never-miss stock picker, soon making deals with the street's scariest fixer/investor (Robert De Niro).
Here "Limitless" and the temporary NZT brain-bumps reference Wall Street's bubble economy, and also set up the battle of wits between brash Eddie and De Niro's master manipulator, a conflict that becomes the movie's most important story thread. (Poor Cornish disappears.)
Burger throws in periodic spurts of violence (cue the Russian mob) to maintain conventional action beats and keep "Limitless" moving. Move, it does. The movie has more energy and imagination than discipline, and it has no ending at all.
Or rather, "Limitless" has the most irksome sell-out finale since . . . "The Adjustment Bureau."
If you believe that Charlie Sheen could walk into a warehouse full of cocaine and hookers and walk out sober and celibate, you'll believe this ending.