Cheers! A cure for the common hangover may have been found - and we have the Russians and the Cold War to thank.

A new pill, RU-21, said to have been first formulated by the KGB so its hard-drinking agents would have an edge on their enemies, is becoming increasingly popular in A-list social circles in New York and Hollywood as a way to avoid the aftereffects of a boozy night.

And a test of the supplement last week by The Post suggests it works, with four volunteers who agreed to take RU-21 giving it a rousing thumbs up.

The volunteers - the authors of this article and their girlfriends - each consumed a similar number of drinks on consecutive evenings, but took RU-21 as directed on the second night on the town.

Headaches, tiredness and irritability were abound on the first morning after, but there were no hangovers and four clear heads the next day.

The conclusion was that with spy technology like this, it's amazing that the Russians lost the Cold War.

Among those who swear by RU-21 are actor Leo Rossi, who played Robert DeNiro's evil cousin in the gangster comedy "Analyze This," and model and actress Beverly Peele, who was once married to hard- living Charlie Sheen.

"There's no magic elixirs in the world, but it works pretty good," said Rossi.

Peele says the supplement is popular among her model friends, as they can hit cocktail parties at night without showing up puffy- eyed to the next morning's photo shoot.

The manufacturers say RU-21 is a mix of vitamin C, carbohydrates and amino acids. It does not prevent drunkenness, but they claim it stops the body from producing an enzyme that turns alcohol into acetaldehyde, a toxin that contributes to the effects of a hangover.

As an herbal-based supplement, it does not require FDA drug approval. It sells mostly online for about $5 for a packet of 20. Pills have to be taken before drinking and after every two drinks.

The American distributor, California-based Spirit Sciences, says it is selling thousands of dollars worth of pills each day, with "numerous" New York customers, according to company chief Emil Chiaberi.

"It makes sense in New York, where entertainment and socializing are such big parts of life," he said.

Critics of RU-21 say the manufacturer's claims have not been scientifically tested and its marketing promotes an irresponsible approach to alcohol use.

"The social context of this thing catching on and causing increased alcohol abuse is very frightening to me," said UCLA psychiatrist and addiction specialist Dr. Reef Karim.

Sip, sip hooray

The Post team tested purported hangover cure RU-21 over two nights, with the supplement taken on the second night:

Howard Breuer, 39: Six vodka shots, L.I. Iced Tea

First morning: Mild hangover, headache, tired

Second morning: "Fine."

Kerri Roepel, 37: Seven vodka shots

First morning: Hung over, headache, body aches

Second morning: "Great."

Todd Venezia, 32: Seven bourbons and a beer

First morning: Head throbbed all day

Second morning: "No hangover, no headache."

Yvonne Westfall, 34: Four bourbons, two margaritas

First morning: Unbearable hangover, felt like a poached egg

Second morning: "Head clear, stomach calm."