The moment when the FBI concluded that pot had got the better of the late rock star is recorded in one of a myriad of files on deceased celebrities released by the US government this week under freedom of information statutes.
The same collection of papers reveals how far the agency went to spy on other celebrities, ranging from Marilyn Monroe - supposedly a Communist - to Liberace, who apparently had a gambling problem.
There has never been any secret about the preoccupation of the US government with Lennon after his arrival in America from Britain with his second wife, Yoko Ono, in 1971. Their political views and high-profile activism - including the famous Montreal "bed-in" in which they expounded on world peace while wearing pyjamas - caused deep suspicion in the Nixon administration.
The surveillance only really ended in 1976 after Lennon won his battle with the Immigration and Naturalisation Service for the right to remain in the US. In possession of his precious green card he vanished into virtual seclusion with his wife at their apartment in the Dakota Building in Manhattan - the scene of his murderfour years later.
In one memorandum from 1972 an FBI agent writes that Lennon wanted a visa extension only so he could "engage in disruptive activities surrounding the Republican convention that renominated Richard Nixon for a second term.
But an informant advised the FBI not to get so exercised about the singer from Liverpool. He said that although Lennon "appears to be radically oriented", he did not give the impression of being seriously committed to any cause, "since he is constantly under the influence of narcotics".
The travails of Lennon as he tried to make America his new home through the 1970s while battling against the suspicions of its government will be explored in a new documentary film.
Due for release in the middle of next year, The US vs John Lennon, to be directed by David Leaf, is described as a chronicle of the surveillance of the ex-Beatle until 1976, when a Democrat, Jimmy Carter, won the presidency. Yoko Ono, who still lives in the same Dakota Building apartment, 25 years after her husband's death, has co-operated on the project. She was also involved in a Broadway musical, Lennon, that opened to poor reviews six weeks ago. The musical lingers on Lennon's battle to win residency in the US. The show failed to impress either critics or theatre-goers and will close after a final performance tomorrow.
This week, the BBC revealed that in November it plans to broadcast for the first time in Britain an hour-long interview that was given by Lennon to Jann Wenner, the founder of Rolling Stone magazine, just after the break-up of the Beatles. The interview will be broadcast on Radio 4.