But in the involuntary manslaughter trial of Dr. Conrad Murray, stemming from Jackson's 2009 overdose death, addiction specialist Dr. Robert Waldman could not say unequivocally whether he believed the singer was addicted to the painkiller.
Waldman was testifying as an expert witness for the defence as it neared wrapping up its case. The claim by Murray's attorneys that the "Thriller" singer was addicted to various drugs and that he engaged in "doctor shopping" is a central part of the defence strategy.
Murray has admitted to giving Jackson nearly daily doses of the powerful anesthetic propofol as a sleep aid at the singer's Los Angeles mansion, and medical examiners found that was the chief cause of his June 25, 2009, death.
But Murray's attorneys argue that the physician was unaware that the singer was getting shots of the addictive painkiller Demerol from a Beverly Hills dermatologist, and that it hampered Murray's efforts to get him to sleep.
Waldman said side-effects of Demerol withdrawal include anxiety and insomnia.
According to medical records presented on Thursday, Jackson received 900 milligrams of Demerol over three days in May 2009, from dermatologist Dr. Arnold Klein.
Klein's records show he also gave Jackson Botox and Restylane for wrinkles and excess perspiration for several months in 2009. Waldman described the Demerol shots as "stiff doses" that were not needed with skin treatment injections.
"I believe there is evidence that he was dependent on Demerol," Waldman said of Jackson, adding that the pop star was "possibly" addicted to the painkiller.
But during an aggressive cross-examination by prosecutors, Waldman could not say for certain that Jackson was addicted to the drug. He also acknowledged that he was not officially certified as an addiction specialist.
Dependence is characterized by a physical need for a drug, while addiction is more serious because it also involves a person continuing with destructive behavior and use of a substance, despite bad consequences, Waldman said.
Murray's attorneys argue that on the day the singer died, Jackson gave himself an extra, fatal dose of propofol.
The doctor, who has pleaded not guilty, faces up to four years in prison if convicted.
