Marijuana will remain a Schedule I drug, the most restrictive category under federal drug control laws. Heroin and LSD are also considered Schedule I drugs.
Schedule II drugs include Ritalin, Adderal and oxycodone.
"Marijuana remains a Schedule 1 controlled substance because it does not meet the criteria for currently accepted medical use in treatment in the United States, there is a lack of accepted safety for its use under medical supervision, and it has a high potential for abuse," the DEA said today.
When the DEA announced its review in April, the American Medical Association told ABC News that the group supported the review "to help facilitate scientific research and the development of cannabinoid-based medicines."
But the DEA has ruled that more research needs to be done to determine the medical effectiveness of marijuana and the agency has loosened the regulations on marijuana research. The DEA plans to increase the number of DEA-registered marijuana growers to "provide researchers with a more varied and robust supply of marijuana."
One petition was submitted in 2011 by former Rhode Island Gov. Lincoln Chafee and former Washington Gov. Christine Gregoire; the other was submitted in 2009 by Bryan Krumm, a psychiatric nurse practitioner in Albuquerque, New Mexico, who helped write New Mexico’s medical cannabis law.
Krumm told ABC News he was disappointed by the DEA's decision and intends to appeal. He said he has more than 1,000 patients in a medical cannabis program that use the drug for Post-Traumatic Stress Disorder (PTSD).
Krumm noted that medical cannabis has "life-saving benefits" and it’s the “only mediation that’s able to rapidly reduce suicidal thinking in most PTSD patients." It can also help individuals undergoing cancer treatments, he added.
“There have been very few reports of significant adverse effects associated with medical cannabis," he said.
Washington Gov. Jay Inslee said in a statement: “I am disappointed that we don’t have a national standard for at least medical marijuana. Regardless, following the will of Washington state voters, we will continue to maintain a well-regulated adult-use marijuana system and continue to allow patients to have access for necessary medicinal purposes."
"I appreciate the DEA’s focus on youth prevention and for allowing more testing centers which will provide more medical research for more informed national policy decisions," Inslee said. "As states continue to legalize medical and recreational marijuana across the country, there is more that the federal government must to do to provide states with legal certainty and empower the operation of safe systems across the country.”
ABC News' Gillian Mohney contributed to this report.