The man who committed the worst mass shooting in modern U.S. history was prescribed an anti-anxiety drug in June, according to The Las Vegas Review-Journal.
The Review-Journal on Tuesday reported that the medication Stephen Paddock was taking can lead to aggressive behavior.
Records from the Nevada Prescription Monitoring Program obtained Tuesday show that Paddock was prescribed 50 10-milligram diazepam tablets.
A physician named Dr. Steven Winkler of Henderson, Nevada wrote Paddock the prescription on June 21.
Paddock purchased the medication – whose brand name is Valium – without insurance at a Walgreens store in Reno the same day.
The gunman was supposed to take one pill daily of diazepam, which is a sedative-hypnotic drug in the class of drugs known as benzodiazepines.
Studies have shown benzodiazepines can trigger aggressive behavior, and, according to drugabuse.com, chronic abuse or use of sedatives can also have negative side effects.
Drugabuse.com said that such consumption of sedatives like diazepam can trigger psychotic experiences.
Dr. Mel Pohl, chief medical officer of the Las Vegas Recovery Center, told the Review-Journal that the drug's effects can also be magnified by alcohol.
"If somebody has an underlying aggression problem and you sedate them with that drug, they can become aggressive," he said from the Netherlands.
"It can disinhibit an underlying emotional state," he continued. "It is much like what happens when you give alcohol to some people ... they become aggressive instead of going to sleep."
Some Twitter users on Wednesday wondered what Paddock’s reported prescription might reveal about why he opened fire on an outdoor concert in Las Vegas last Sunday.
Authorities found Paddock dead last weekend in his hotel room on the 32nd floor of the Mandalay Bay Resort and Casino.
Paddock’s attack beforehand killed at least 59 people and wounded at least 527 others, and speculation has since run rampant over his motives.