Parents of toddlers lock up medicines so their children do not have access to dangerous drugs. Now experts are advising parents of teens to do the same thing.

A new study from the National Center on Addiction and Substance Abuse found that teens say it is easier to obtain prescription drugs than cigarettes, beer, or marijuana. One-third of the teens in the study who abuse such drugs obtain them from their own homes. Parents are often unaware teens are raiding family medicine cabinets because teens often steal just a few pills at a time.

Researchers in this latest government study interviewed 1,000 students ages 12 to 17 and 300 parents between April and June. Nearly half of the older teens reported knowing at least one friend who was abusing prescription drugs.

Illegal drug use among teenagers has declined 25 percent since 2001, but teen prescription drug abuse is increasing, according to the Office of National Drug Control Policy. Opiates such as Vicodin and OxyContin, which are chemical cousins of heroin and morphine, are particularly popular with teens. Teens are prone to addiction because the human brain does not fully mature until age 24.

"This has quietly and insidiously grown into a big problem," said spokesperson for the agency, Tom Riley. "It's not the creepy guy in an overcoat pushing drugs - this is about medications that are in your home. ... Teens are getting drugs from their parents' or grandparents' medicine cabinets."

Teens can also buy almost any drug they want from Internet pharmacies without doctors' prescriptions.

New legislation sponsored by California Senator Dianne Feinstein would require any business selling controlled substances on the Internet to register with the Drug Enforcement Agency. This measure passed in the House of Representatives and is now pending in the Senate.