The White House Office of National Drug Control Policy (ONDCP) says that new research shows that the average potency of marijuana sold in the U.S. has roughly doubled since 1983 -- a far cry from drug czar John Walters' past assertion that pot has become up to 30 times stronger.

The report from the University of Mississippi's Potency Monitoring Project said the average THC content in seized marijuana samples was 8.5 percent, up from about 4 percent in 1983. ONDCP and the National Institute on Drug Abuse (NIDA) said that THC content has "reached the highest-ever levels since scientific analysis of the drug began in the late 1970's."

The report was based on an analysis of 59,369 cannabis samples, 1,225 hashish samples, and 443 hash oil samples gathered by law-enforcement agencies since 1975.

"This new report serves as a wake-up call for parents who may still hold outdated notions about the harms of marijuana," said Walters. "Evidence now tells us that the higher-than-ever potency of today's marijuana translates into serious health consequences for teens."

ONDCP suggested that higher marijuana potency could be contributing to increases in teens seeking treatment for marijuana use and marijuana-related emergency-room visits.

In 2002, Walters wrote a column claiming that average THC content in marijuana had risen to 14 percent and that "the potency of available marijuana has not merely 'doubled,' but increased as much as 30 times."