A new high for marijuana in U.S.

The marijuana being sold across the United States is stronger than ever, which could explain a growing number of medical emergencies that involve the drug, government drug experts Wednesday.

Analysis of seized samples of marijuana and hashish showed that more of the cannabis on the market is of the strongest grade, the White House and National Institute for Drug Abuse said.

They cited data from the University of Mississippi's Marijuana Potency Project showing the average levels of THC, the active ingredient in marijuana, in the products rose from 7% in 2003 to 8.5% in 2006. The level had risen steadily from 3.5% in 1988.