As the years tick by, Sumner Redstone just gets more optimistic. Earlier this year the 84-year-old said he planned to live another 50 years; two years ago he was predicting another 20. His age has been in the spotlight lately because of the recent public spat with his daughter over his succession plans, but the controller of Viacom (VIAB) and CBS (CBS) has lately been getting a bit of help in the form of a little-known superjuice called MonaVie. “It’s a miracle drug,” he told Fortune. “I feel great.”

A dark-purple elixir with a cult-like following, MonaVie is an antioxidant-rich concoction whose main ingredient is the Brazilian açai berry (pronounced ah-sigh-ee), long touted among health nuts for its anti-aging ingredients. Vitamin-water it’s not: MonaVie costs $40 a bottle, and you can’t get it in stores; it’s marketed only through the company’s network of thousands of individuals who sell it out of their homes (think Avon or Tupperware).

Redstone first heard of the juice from Viacom exec Bill Roedy on a trip to Germany in January. After learning that his butler’s sister-in-law was a devotee too, Redstone ordered some up and started drinking four ounces a day. “Since I’ve been on MonaVie I haven’t taken a sleeping pill,” he says.

Redstone says he hasn’t taken a sleeping pill in months.

He even considered investing in Utah-based MonaVie after its CEO, Dallin Larsen, came to visit him at his Beverly Hills mansion. Redstone decided against it—because it would present a conflict of interest to recommend it to friends—but Larsen, a veteran nutritional-products salesman who founded the company in 2005, has no better ambassador. At a recent party, Redstone gave bottles to Bill Clinton and celebrity chef Wolfgang Puck. “Just about every friend I have is on it,” Redstone says—a group he says includes Viacom and CBS board members as well as cancer survivor and former junk-bond king Michael Milken. (It can also be found in the clubhouse of the Boston Red Sox; pitcher Jonathan Papelbon is a fan.)

For more on CBS, watch this Fortune video:

So is it a fad, or is there something to it? Nothing proves that MonaVie cures any ailment, but in one of the first academic studies of açai’s benefits, University of Florida researcher Stephen Talcott found that the berry’s antioxidants destroyed leukemia cells in a laboratory. But Talcott has since distanced himself from MonaVie and its junkies.

Larsen is careful not to cross the line. “It’s not a drug,” he says. He touts the juice as a way to “increase energy in a natural way” and to alleviate “the everyday aches and pains from inflammation.”

Redstone says he’s never felt better. “I know I look a lot younger than I am,” he says. “I feel like I’m 40 years old.”