EXCLUSIVE: Marilyn Monroe's Secret Drug Addiction Shocker — Experts Blame Agonizing Medical Condition for Bombshell's Deadly Pill-Popping

Marilyn Monroe's hidden battle with a debilitating medical condition may have played a devastating role in the drug dependency that overshadowed the final years of the Hollywood icon's life, RadarOnline.com can reveal.

The devastating theory is held by experts we consulted who are examining the star's private struggles.

Monroe, who died aged 36 in 1962 and would have turned 100 on June 1, remains one of the most famous figures in movie history.

Celebrated for her performances, glamour, and highly publicized relationships, she also endured years of severe endometriosis – a painful disorder in which tissue similar to the lining of the uterus grows outside the womb.

The condition was poorly understood during her lifetime, and experts said the lack of effective treatment contributed to chronic pain, repeated hospitalizations, fertility problems, and an increasing reliance on powerful medication.

Anthony Summers, author of the 1985 biography Goddess: The Secret Lives of Marilyn Monroe, wrote about Monroe's fight with the agonizing condition: "(It) was so severe that it destroyed her marriages, her wish for children, her career, and ultimately her life. In days before effective conservative surgery or effective medical therapies, it led to progressively increasing use of strong analgesics, tranquilisers and hypnotics – and drug dependency."

Bryan Johns, president and chief executive of the ICON Collection, which contributed extensively to the exhibition Marilyn Monroe: Hollywood Icon at the Academy Museum of Motion Pictures, said Monroe's health battles were frequently dismissed.

He said: "She had terrible, debilitating endometriosis and was hospitalized and under medical supervision for that condition throughout her life. Although she had communicated her health issues to the studio, oftentimes the studio would refute this and accuse her of making it up in order to try and keep her under their control – defining the narrative to the gossip columnists."

And a source familiar with Monroe's medical history told Radar: "What people often interpreted as unreliability or emotional instability was, in many cases, linked to severe pain and the medications she relied upon to cope with it. It basically caused her to become a tablet junkie."

Another Monroe historian said, "The tragedy is that she was living in an era when women were expected to suffer in silence. The treatments available were limited, and dependency on prescribed drugs became increasingly common for patients with chronic conditions."

According to the Mayo Clinic, endometriosis affects more than 11 percent of women in the United States.

Monroe was described in a 2008 paper published by the National Library of Medicine as "one of the most famous sufferers from endometriosis."

The condition also compounded Monroe's heartbreak over her inability to have children.

Having spent her childhood in orphanages and foster homes before being discovered as a model at 18, she longed to create a family of her own.

Johns added: "She worked extremely hard at creating 'Marilyn Monroe' which was a character for her; it was 'Marilyn Monroe' that would play the part in the film, Norma Jeane playing Marilyn Monroe playing the part. People who worked with her – directors, producers, studio executives – said they'd never seen another actor who worked harder than she did, wanting to 'be ready' for any opportunities that might come her way."