Marijuana Poses More Health Risks

Marijuana potency increased last year to the highest level in more than 30 years, posing greater health risks to people who may view the drug as harmless, according to a report released Thursday by the White House.

The latest analysis from the University of Mississippi's Potency Monitoring Project tracked the average amount of THC, the psychoactive ingredient in marijuana, in samples seized by law enforcement agencies from 1975 through 2007. It found that the average amount of THC reached 9.6 percent in 2007, compared with 8.75 percent the previous year.

The 9.6 percent level represents more than a doubling of marijuana potency since 1983, when it averaged just under 4 percent.