It has long been suspected that Hitler's frenzied speeches were fuelled by cocaine and other powerful stimulants.
Now, the true extent of his drug habit has been laid bare in a daring new book that claims the Nazi leader was a gibbering "super-junkie" whose veins were all but destroyed by thousands of opiate injections in the dying days of World War Two.
According to Norman Ohler, an award-winning German author, the Fuhrer became addicted to a heroin-like substance called Eukodel which was prescribed following a nervous breakdown in 1944.
Ohler's book Blitzed: Drugs in Nazi Germany, which British historians have praised as a "remarkable" work of research, argues that the heroin-like opiate was largely to blame for Hitler's erratic and paranoid behaviour towards the end of his life.
It brings to light extracts from the journal of Dr Theo Morell, Hitler's personal physician, who once complained he could no longer inject the drug as nearly all of his patient's veins had collapsed.
"'I cancelled injections today, to give the previous puncture holes a chance to heal," one entry reads.
It continues: "Left inside elbow good, right still has red dots (but not pustules), where injections were given."
Ohler says Hitler began the drugs regime after narrowly surviving the 1944 assassination attempt known as Operation Valkyrie, in which the German resistance planted a bomb in a briefcase under his desk.
The explosion shattered both of Hitler's eardrums, riddled his body with splinters from a wooden table that shielded him from the blast and turned him into a nervous wreck.
"I'm afraid that from 1944 onwards, Hitler did not spend a single day sober," Ohler told the Telegraph.
"Before then, he was a very public person... but the attempt on his life left him withdrawn, paranoid and anxious.
"He demanded that Dr Morell restore him to his former confident self, so from that point on he received thousands of injections - most frequently Eukodol, which is like heroin but with a greater potential to make you euphoric."
In an extract from the book itself, Ohler writes: "Germany, land of drugs, of escapism and worldweariness, had been looking for a super-junkie.
"And it had found him, in its darkest hour, in Adolf Hitler."
As the drugs took their toll, Hitler's decision-making became more erratic.
Antony Beevor, a British war historian, said the book's findings explained Hitler's "completely irrational" military tactics during the Battle of the Bulge, which was the dictator's last-ditch attempt to defeat the allies.
"All of these elements show how he was really no longer in control of himself, but he was still in control of the German armies," he told the BBC's Today programme.
Beevor, who has written extensively about World War Two, said the book was a "remarkable work of research" which even offered clues as to why Britain abandoned an attempt to kill Hitler in 1944.
"What we're seeing is an explanation of the fact why the British in 1944 decided no longer to attempt to assassinate Hitler," he said.
"Operation Foxley was cancelled because they realised at this particular stage that the Allies would win the war more rapidly with Hitler in command, than Hitler being replaced by somebody else."
The Nazis stumbled from one defeat to the next under their drug-addled leader until April 1945, when the supply of drugs in his final bunker ran dry.
As Soviet troops gathered around the Nazi leader's headquarters, the Fuhrer's physician sent raiding parties into Berlin's war-torn city centre on motorcycles to scour pharmacies for more drugs.
Their efforts failed and Hitler committed suicide shortly after, on April 30 1945.
Ohler's book, which will be published on October 6, also discusses the widespread consumption of a meth-like substance called Pervitin among Nazi soldiers.
"The massive abuses of methamphetamine, which we today call crystal meth, by the German army shows that the enemy number one were not the British or the French or the Russians, but fatigue," Mr Ohler told the Today programme.
"The German army was trying to win the battle against sleep. That's why they used it and in the beginning it worked wonders in the attack on Poland and in the so-called Blitzkrieg."