Americans are using less cocaine and more marijuana than before, according to new data on illegal US drug use.

Pulling from numerous national studies, data on illegal drug use were collected nationwide from 2000 to 2010 as part of a study done for the White House Office of National Drug Control Policy. Between 2006-2010, cocaine use was cut in half across the US, while the same time period revealed a 30 percent increase in marijuana use.

Heroin use remained stable throughout the decade, the study found. Consumption of methamphetamine rose sharply during the first half of the decade before declining, but end-of-decade data on meth-use was not solid enough for researchers to make definitive statement on the overall trend for the decade.

Throughout the decade, Americans spent $100 billion on cocaine, heroin, marijuana and methamphetamine every year, according to the study, which is published on the Office of National Drug Control Policy's website. While the sum of money spent annually on illegal drugs stayed the same throughout the decade, the drugs the money was spent on changed, the researchers found.

"Our analysis shows that Americans likely spent more than $1 trillion on cocaine, heroin, marijuana and methamphetamine between 2000 and 2010," said lead study author Beau Kilmer, co-director of the RAND Drug Policy Research Center.

Because the study only ran through 2010, researchers said Colorado and Washington state's recent legalization of marijuana for recreational use was not factored in, nor was a recent spike in heroin use.

Still, the data will be valuable for policy makers, drug treatment centers and researchers, the study authors said.

"Having credible estimates of the number of heavy drug users and how much they spend is critical for evaluating policies, making decisions about treatment funding and understanding the drug revenues going to criminal organizations," Kilmer said. "This work synthesizes information from many sources to present the best estimates to date for illicit drug consumption and spending in the United States."

The researchers said that similar and more accurate studies in the future will be more difficult now that the government has canceled the Arrestee Drug Abuse Monitoring Program (ADAM). ADAM data were used in the compilation of this study's results.

"The ADAM program provided unique insights about those who abused hard drugs and how much they spent on these substances," said study co-author Jonathan Caulkins of Carnegie Mellon University. "It's a tragedy that 2013 was the last year for ADAM. It is such an important data system for understanding drug problems."