Schaffel, who produced Jackson's "Private Home Movies" in 2003, said his friend's addiction to Demerol began as early as 1984, when the pop star suffered burns when his hair caught fire filming a Pepsi commercial. He was later was treated at the Betty Ford Clinic.
In 2002, Jackson was ordered to undergo a medical examination after he failed to show up in a California court room in a trial over breach of contract because the pop star said he had a spider bite.
"He had the IV stuff back then," said Schaffel, "It wasn't a spider bite. It was an IV he pulled out his leg. The needle broke off."
Jackson had complained of a series of medical maladies since the beginning of the 2002 civil trial in which he was accused of backing out on a pair of millennium concert performances.
He arrived at the Santa Monica courthouse on crutches and wearing only one shoe, telling reporters that he had awakened to find his left foot too swollen to fit in a shoe.
At the time, Jackson claimed the bite had not come from one of the tarantulas he kept as pets at his Neverland Ranch, but rather a small spider when the compound was being fumigated.
It has been widely reported that in addition to Demerol and Oxycontin, Jackson also abused the anti-anxiety drug Xanax and the anti-depressant Zoloft in the months before his death.
Demerol, a powerful prescription painkiller and opioid, often used in childbirth labor, is highly habit-forming.
A well-known side effect of Demerol and other pain medications is respiratory depression, according to Sanjay Sethi, chief of pulmonary, critical care and sleep medicine at University at Buffalo in New York.
"A large dose, especially if given intravenously, can act on the respiratory center of the brain, reduce respiratory drive, cause cessation of breathing, leading to cardiac arrest because of lack of oxygen," Sethi told ABCNews.com. "Antidotes are available, but they have the best effect only when used prior to cardio-respiratory arrest."
Both rock icon Elvis Presley and movie star Heath Ledger died of combination drug overdoses, the former in 1977 and the latter in 2008.
Lisa Marie Presley, who was briefly married to the pop star, said on her MySpace page that Jackson feared he would die like Elvis.
"At some point he paused, he stared at me very intensely and he stated with an almost calm certainty, 'I am afraid that I am going to end up like him, the way he did,'" wrote Presley.
According to the U.S. Drug Enforcement Administration, more than 8,500 deaths nationwide involved prescription pain relievers in 2005, an increase of 114 percent since 2001.
In addition, nearly one-third of individuals who began abusing drugs in the past year reported their first drug was a prescription drug. About 19 percent of those were opioids.
Jackson's family lawyer, Brian Oxman, compared the star's death to that of Anna Nicole Smith, who died in 2007 of a drug overdose.
"This family has been trying for months and months and months to take care of Michael Jackson," said Oxman. "The people who have surrounded him have been enabling him."
But producer Schaffel said it was a coterie of "pseudo doctors," including a South Florida physician and a New York City anesthesiologist, who provided Jackson with drugs, often prescribed to others.