The memo notes that efforts should focus on prosecution of significant marijuana traffickers. "Marijuana distribution in the United States remains the single largest source of revenue for the Mexican cartels," the memo states.
The new policy is not without its critics, including some federal lawmakers who see it as a weakening in the war against Mexican drug cartels, the AP said.
"We cannot hope to eradicate the drug trade if we do not first address the cash cow for most drug trafficking organizations -- marijuana," said Rep. Lamar Smith of Texas, the ranking Republican on the House Judiciary Committee.
One health expert said the policy change was good, noting concerns about marijuana should be based on science and not the fear that any drug will be abused.
"I was never sure why there was an issue," said Kenneth W. Goodman, a professor of medicine at the University of Miami Miller School of Medicine, and co-director of the university's ethics programs. "We have a long track record about making judgments about drugs based on research."
"My view has always been whether you should use opiates or aspirin or antibiotics or marijuana or anything depends on the research," he said. "If there is evidence that shows that something works and it's controlled by physicians, then what's the problem?"
For more on marijuana, visit the U.S. National Library of Medicine.
SOURCES: Oct. 19, 2009, memo, U.S. Department of Justice, Washington, D.C.; Kenneth W. Goodman, Ph.D., professor of medicine, University of Miami Miller School of Medicine, co-director, University of Miami ethics programs; Allen St. Pierre, executive director, NORML, Washington, D.C.; Associated Press