There are enough organic potions and natural remedies on Robert Downey Jr.'s coffee table to stock an aisle at Whole Foods. Shriveled, rooty-looking things in Ziploc bags. Jars filled with herbal pills as big as bullets. He's sitting cross-legged on the floor next to all of these unusual items in the living room of the London townhouse he's been renting while shooting his latest movie, an elementary detective story called Sherlock Holmes. It's 2 o'clock in the afternoon, but with his hair in full bedhead bloom, Downey looks like he could use a pick-me-up. He reaches for a bottle and shakes a dozen gelcaps into his palm, then stuffs them into his mouth. ''Brain formula,'' he mumbles as he gulps them down.

They must be working. This year, thanks to a series of clever choices, Downey has pulled off one of the smartest second acts in recent showbiz history. After doing just about everything humanly possible to destroy a once-promising career — including spending the better part of a decade in courtrooms and even jail cells — he's finally fulfilling his potential. He's become a movie star. At 43. For starters, he's at the red-hot center of a humongous new action franchise, Iron Man, which has grossed more than half a billion dollars worldwide since opening last May. He followed that in August by doing something few actors have dared since Jolson — blackface — in the Ben Stiller comedy Tropic Thunder, which grossed $110 million. Next spring, he'll be costarring with Jamie Foxx in The Soloist, Atonement director Joe Wright's drama about a journalist who befriends a homeless musical genius he finds pushing a shopping cart around L.A. (Downey's performance was starting to generate Oscar buzz — the most since his nomination for Chaplin in 1993 — but then The Soloist was moved from its November release date to next April.) And now, here in London, there's Warner Bros.' latest franchise launch Sherlock Holmes — directed by that Guy getting divorced from Madonna — which Downey just started shooting two weeks ago.

''Why am I having this year?'' he ponders, chasing down the formula with a swig of mineral water. ''To tell you the truth, I haven't fully digested what's happened to me before, during, and after Iron Man. Tropic Thunder seems like it happened 25 minutes ago. Time is not entirely linear. It's all so associative. If Ben Stiller called me today and said we needed to shoot more scenes, I'd get my jacket and go. But I do know that I don't want to waste any more time. That's why I'm putting my nose to the grindstone. That's why I'm cranking them out.''

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