A 50-year mystery over the 'cursed bread' of Pont-Saint-Esprit, which left residents suffering hallucinations, has been solved after a writer discovered the US had spiked the bread with LSD as part of an experiment.

In 1951, a quiet, picturesque village in southern France was suddenly and mysteriously struck down with mass insanity and hallucinations. At least five people died, dozens were interned in asylums and hundreds afflicted.

For decades it was assumed that the local bread had been unwittingly poisoned with a psychedelic mould. Now, however, an American investigative journalist has uncovered evidence suggesting the CIA peppered local food with the hallucinogenic drug LSD as part of a mind control experiment at the height of the Cold War.

The mystery of Le Pain Maudit (Cursed Bread) still haunts the inhabitants of Pont-Saint-Esprit, in the Gard, southeast France.

On August 16, 1951, the inhabitants were suddenly racked with frightful hallucinations of terrifying beasts and fire.

One man tried to drown himself, screaming that his belly was being eaten by snakes. An 11-year-old tried to strangle his grandmother. Another man shouted: "I am a plane", before jumping out of a second-floor window, breaking his legs. He then got up and carried on for 50 yards. Another saw his heart escaping through his feet and begged a doctor to put it back. Many were taken to the local asylum in strait jackets.

Time magazine wrote at the time: "Among the stricken, delirium rose: patients thrashed wildly on their beds, screaming that red flowers were blossoming from their bodies, that their heads had turned to molten lead."

Eventually, it was determined that the best-known local baker had unwittingly contaminated his flour with ergot, a hallucinogenic mould that infects rye grain. Another theory was the bread had been poisoned with organic mercury.

However, H P Albarelli Jr., an investigative journalist, claims the outbreak resulted from a covert experiment directed by the CIA and the US Army's top-secret Special Operations Division (SOD) at Fort Detrick, Maryland.

The scientists who produced both alternative explanations, he writes, worked for the Swiss-based Sandoz Pharmaceutical Company, which was then secretly supplying both the Army and CIA with LSD.

Mr Albarelli came across CIA documents while investigating the suspicious suicide of Frank Olson, a biochemist working for the SOD who fell from a 13th floor window two years after the Cursed Bread incident. One note transcribes a conversation between a CIA agent and a Sandoz official who mentions the "secret of Pont-Saint-Esprit" and explains that it was not "at all" caused by mould but by diethylamide, the D in LSD.

While compiling his book, A Terrible Mistake: The Murder of Frank Olson and the CIA's Secret Cold War Experiments, Mr Albarelli spoke to former colleagues of Mr Olson, two of whom told him that the Pont-Saint-Esprit incident was part of a mind control experiment run by the CIA and US army.

After the Korean War the Americans launched a vast research programme into the mental manipulation of prisoners and enemy troops.

Scientists at Fort Detrick told him that agents had sprayed LSD into the air and also contaminated "local foot products".

Mr Albarelli said the real "smoking gun" was a White House document sent to members of the Rockefeller Commission formed in 1975 to investigate CIA abuses. It contained the names of a number of French nationals who had been secretly employed by the CIA and made direct reference to the "Pont St. Esprit incident." In its quest to research LSD as an offensive weapon, Mr Albarelli claims, the US army also drugged over 5,700 unwitting American servicemen between 1953 and 1965.

None of his sources would indicate whether the French secret services were aware of the alleged operation. According to US news reports, French intelligence chiefs have demanded the CIA explain itself following the book's revelations. French intelligence officially denies this.

Locals in Pont-Saint-Esprit still want to know why they were hit by such apocalyptic scenes. "At the time people brought up the theory of an experiment aimed at controlling a popular revolt," said Charles Granjoh, 71.

"I almost kicked the bucket," he told the weekly French magazine Les Inrockuptibles. "I'd like to know why."