Singer Janet Jackson and the rest of the Jackson clan were unaware that Michael Jackson was using propofol, a powerful sedative typically used in operating rooms, she told ABC News' Robin Roberts in an exclusive interview.
"That was, that was a shocker to me and it just -- that's serious," Jackson said. "That's heavy. That's heavy. None of us knew to that extent."
Toxicology results showed that Michael Jackson had lethal amounts of propofol in his system when he died, along with a cocktail of other prescription drugs. His death was ruled a homicide.
But the family was not naive about her brother's drug problem, Jackson said, adding that she reached out to him throughout the years but was unsuccessful.
"I did," she said. "Of course, that's what you do. Those are the things that you do when you love someone. You can't just let them continue on that way. And we did a few times. We weren't very successful."
Jackson said her brother understood that the family's motives for the interventions were out of love.
"How do I say this? Understanding. I guess that will be the best way to -- understood that it was out of love, because of caring. But when it's something like that, people can tend to be in denial," she said.
When asked if her brother was in denial about his addiction, she replied, "Possibly."
"I wish he could answer this question for you and not me," she said. "I felt that he was in denial."
The five-time Grammy award-winning artist said that she was "incredibly close" to older brother Michael; but the siblings went through long stretches without seeing one another, and Michael slowly succumbed to a dangerous spiral of drugs and addiction.
"You can't make 'em drink the water. ... I'm a true believer in prayer, a big believer in prayer -- but it's, it's something that you can't do for them. Something they have to do for themselves," she said.
Michael Jackson's personal physician, Dr. Conrad Murray, has admitted to administering propofol but has denied giving Michael anything that should have killed him.
Murray is still under investigation in Los Angeles. The district attorney's office has yet to announce any charges against him in Jackson's death, but on Monday, Murray appeared in court on charges that he owes more than $14,000 in child support.
Murray agreed to start making payments to avoid jail time but claimed he had to close his practice because of threats he received after Jackson died.
Janet Jackson said she wants to see that Murray is never allowed to practice medicine again.
"He was the one that was administering," told Roberts. "I think he is responsible."
For Jackson, her interventions with Michael through the years echoed the trials of her first marriage to James DeBarge, who has admitted to being addicted to prescription medication.
"It kinda goes back to my first relationship, something that you have to want. ... it's something they have to want," she said of her desire to rid both Michael and DeBarge of their addictions.
At 18, Jackson's marriage to DeBarge, part of a family singing sensation billed as the next Jackson 5, was an act of rebellion. The two eloped without the approval of her parents.