“For many years, I have cautiously peered from behind the face of a man known as Cary Grant. The protection of that facade was both an advantage and a disadvantage. If I couldn’t see out, how could anyone see in?”

That’s how icon Cary Grant disclosed an identity crisis that prompted him, at age 53, to submit to 100 LSD therapy sessions. The revelation comes in “Becoming Cary Grant,” a documentary airing Friday on Showtime that gets at the heart of who the man born Archibald Leach really was.

It was 1958. After a long career as the star of comedies such as “The Philadelphia Story” and “Bringing Up Baby,” Grant had reinvented himself as Alfred Hitchcock’s new go-to leading man in “To Catch a Thief.” His personal life, however, left him wanting. Two early marriages had ended in divorce and the actor, who had also lived on and off for 12 years with film star Randolph Scott, was frustrated by his inability to connect with women.

“He was unable to have a relationship. They were all falling apart,” said filmmaker Mark Kidel.

Grant’s third wife, Betsy Drake, introduced him to Beverly Hills, Calif., physician Mortimer Hartman. Drake “took LSD to cure herself of alcoholism,” according to Kidel, and Hartman was able to obtain the tablets, still legal until 1966, directly from a Swiss pharmaceutical company.

Grant ended up having 100 LSD treatments with Hartman — not a psychiatrist, but a radiologist — over three years.

“The fact that the sessions lasted five to six hours suggests that the doses were not very strong,” Kidel said. “Trips normally last 12 hours or so . . . What is remarkable is that he persevered over three years. LSD takes you to the basement of your psyche.”

Grant, who referred to Hartman as “my wise Mahatma,” didn’t keep the sessions a secret, proclaiming their value to women’s magazines such as Good Housekeeping.

The big take-away, Grant says in the film, was that “LSD made me realize I was killing my mother through . . . relationships with women. I was punishing them for what she had done to me.”

His relationship with his mother, Elsie, was fraught. Haunted by the death of her son John, of tuberculous meningitis at age 1, Elsie tried to substitute her second boy, Archie, for the dead child, dressing him in baby clothes and curling his hair well past infancy. “For a while I wasn’t sure if I was a boy or a girl,” Grant says.

At 9, Archie came home one day in Bristol, England, and found his mom gone — at a resort, his father said. She never returned. “[Grant] thought she died,” said Kidel. “She was never spoken of again.”

Having rechristened himself Cary Grant, the actor did not discover what really happened to his mother until he was 30. The admissions book from the Bristol Lunatic Asylum reveals Elsie was committed in 1915. The diagnosis was listed as “mania,” but it was not made by a doctor or mental health professional. Mrs. Leach was committed on her husband’s testimony alone.

Grant’s mother stayed in the asylum for 20 years. The actor freed her in 1935, the same year his father died. So much time had passed that Grant had to convince her who he really was.

If the LSD experiments did not entirely solve Grant’s problems with women (he married two more times after divorcing Drake, to actress Dyan Cannon and then to p.r. agent Barbara Harris), they apparently did set him free. The actor, who died following a massive stroke in 1986, left $10,000 to Hartman in his will.

Grant told Look magazine of LSD in 1959, “I learned to accept the responsibility for my own actions and to blame myself and no one else for circumstances of my own creating. At last I am close to happiness.”