A new Department of Justice report says American Indian substance abuse levels are higher than those for any other demographic group, with marijuana the most widely available drug on reservations.

The report, conducted by the department's National Drug Intelligence Center, is an assessment of the threat posed from drug trafficking organizations, criminal groups, and gangs that distribute drugs on reservations.

According to the study, Mexican drug trafficking organizations are the main suppliers and producers of the drugs available on reservations, and these organizations "pose the greatest organizational threat to Native American communities across the United States."

The agency predicted that that most reservations around the country will experience increased drug availability and abuse in the near future, largely because of poor socio-economic conditions within reservation communities and a lack of resources available for law enforcement, drug treatment programs and drug education campaigns.

"Without a comprehensive national-level strategy aimed at dedicating greatly needed resources to combating drug trafficking and abuse in Indian Country, including improved data collection methods regarding Indian Country, the overall illicit drug situation on most reservations will deteriorate," the report said.

The study's authors reported the main drugs for which Native Americans sought treatment between 2002 and 2006, with marijuana leading the list. That drug is followed by methamphetamine, cocaine, prescription drugs and heroin. Methamphetamine treatment increased 60 percent between 2002 and 2006.