Despite efforts by governmental agencies to control illegal Internet sales of prescription-free drugs, a large majority of 365 Internet sites continue to advertise or sell them, according to a study made by the National Center on Addiction and Substance Abuse at Columbia University (CASA).

Last year there were 581 sites trying to sell or advertise prescription-free drugs, Joseph A. Califano Jr., director of CASA, said. The new report found 206 sites advertising drugs and 159 sites selling them.

The list of drugs sold illegal on the Internet include generic versions of opiates like OxyContin, methadone and Vicodin , which are known as painkillers; benzodiazepines like Xanax and Valium prescribed for anxiety and stimulants like Ritalin and Adderall.

Federal law forbids sales of dangerous medications without a prescription from a doctor. However, the Internet makes it possible for drug dealers to ship the drugs from foreign countries in disguised packages.

The bad news is that these drugs are available for anyone of any age “with the click of a mouse,” Califano said, adding that “the Internet is a pharmaceutical candy store for teenagers and college students.” According to a 2005 survey, nearly one in five teenagers had abused prescription drugs in their lifetime.

Another reason of concern is that these sites frequently open up for a short time then re-open under a different name, which makes it harder to track them all.

The study findings prompted CASA to recommend Internet search engines to block advertisements for controlled prescription drugs that do not come from licensed and certified pharmacies.

Moreover, in April the U.S. Senate passed the Ryan Haight Online Pharmacy Consumer Protection Act, which calls for federal certification of online pharmacies and prohibits the delivery, distribution, or dispensing of controlled substances online without a prescription issued by a practitioner who has previously conducted at least one in-person medical evaluation. The Act waits for House approval.