Houston would go to rehab twice before she declared herself drug-free to Oprah Winfrey in 2009.
But the damage might have already been done.
Dr. Karen Miotto, director of addiction medicine services at Ronald Reagan UCLA Medical Center, says long term substance abuse can weaken the heart.
"What is notable about cocaine is cocaine can constrict the blood vessels, and so what happens is the heart is working very hard against resistance," Miotto said.
The cause of Houston's death is still under investigation. But experts say people with a history of substance abuse often have a higher tolerance for medication, so they may take more. When mixed with alcohol, it can have a devastating impact.
"Both of these drugs can impair your memory, so you can start out by thinking, 'I took my medication,' but because of the combination, you may not even remember," so you think, you need another dose or one more dose," Miotto said.
Drugs and alcohol kill by slowing a person's ability to breath and cutting off oxygen to the brain. Witnesses say they saw Houston drinking champagne the night before her death.
The side effects of one particular prescription drug may not be that significant on their own, but when combined with other drugs or alcohol, the side effects can be magnified and even deadly.
Dr. Miotto says prescription drug abuse in Los Angeles County kills more people than car accidents.
