A new report says more than 15 million Americans are abusing controlled prescription drugs.

The National Center on Addiction and Substance Abuse says that number is larger than the combined number of people abusing cocaine, hallucinogens, heroin and inhalants.

The organization's president, Joseph Califano, says the biggest problem is among the nation's youth. Califano says the number of teens abusing prescription drugs has tripled in the past decade.

Califano, who was a top official in the Carter administration, says parents must take responsibility for their children's abuse of drugs, but physicians also must be held accountable. Califano says doctors should be checking the drugs their patients are taking before writing out a prescription.