No one has confirmed whether Staff Sgt. Robert Bales was using the drug, known as Mefloquine. But the drug has been linked to dangerous side effects - including depression, psychosis, and suicidal thoughts.
In 2009, the Army ordered that the drug not be given to soldiers who had suffered traumatic brain injuries.
And a few days after the Afghan massacre, Jonathan Woodson, assistant secretary of defense for health affairs, ordered an emergency evaluation of the military's use of Mefloquine to assure troops were not getting the drug inappropriately.
Bales is charged with killing 17 Afghan civilians - and his attorney is investigating a link between the drug and the accusations against his client, who suffered a traumatic brain injury while serving his third tour of combat in Iraq, according to earlier reports.
"I know there's a lot of discussion about the malaria drug, and I don't know yet (whether Bales was taking it)," says the attorney, John Henry Browne. "We have to get his medical records. And I don't know. I wouldn't be surprised. But I don't know that."
He says he expects to get Bales' medical records within the next two weeks.
Mefloquine, also known as Lariam, has been associated in several suicides and murders in the U.S. military.
Grim psychiatric side effects, including problems with psychotic behavior, paranoia and delusions, are some of the complications that arise from the use of Mefloquine.