Scandrick tested positive for MDMA, which is also known as Ecstasy or Molly, league sources told ESPN's Ed Werder.
While MDMA alone would be considered a drug of abuse and would not subject Scandrick to suspension for a first-time positive test, the drug sometimes contains an amphetamine component, which does fall under the league's PED policy and led to Scandrick's punishment.
Scandrick became the 21st player of 104 suspended for performance-enhancing drugs to test positive for MDMA.
Sources told Werder that the violation occurred while Scandrick was vacationing in Mexico with an ex-girlfriend, whom he has claimed persuaded him to add a substance he didn't realize was on the banned list into a cocktail they were drinking.
According to a source with knowledge of the situation, Scandrick failed a drug test in April and appealed its findings. The league rendered its decision Monday. He will lose approximately $1 million through four missed game checks and a signing bonus repayment.
In a statement released through his agent, Ron Slavin, Scandrick insisted he did not knowingly take a banned substance.
"I would like to apologize to my children, my family, the Jones family, my coaches, my teammates and my fans," Scandrick said in the statement. "Failing a drug test is far out of my character, and although I never knowingly took a performance-enhancing drug/banned stimulant while on vacation in Mexico, I take full responsibility for what goes in my body and more importantly for the embarrassment of a failed drug test. It's my goal by issuing this statement to clear my name and more importantly to be judged by what happens to me in the future.
"I hope that my family, my Cowboys football family and all my fans can forgive me for this situation. I look forward to a successful 2014 season."
He will be eligible to return to the active roster on Sept. 29. Scandrick also can participate in all preseason practices and games.
Scandrick, a seven-year veteran, is coming off the best season of his career. He won the starting job after Morris Claiborne was injured during the preseason and performed well, serving as a bright spot on a unit that ranked last in the league in total defense. Scandrick and Claiborne, who missed the preseason opener due to tendinitis in his right knee, were competing for a starting job again this summer.
Slavin blamed the suspension on the NFL and NFL Players Association's failure to come to an agreement on human growth hormone testing, which has been a point of contention since a new collective bargaining agreement was passed in 2011.
"I do not excuse Orlando having tested positive for a banned stimulant," Slavin said in a statement. "The current rules are what they are, and a player is responsible for what is in his body. However, I would like it known that it is my understanding that if the current proposed agreement related to HGH testing would have already been instituted, a very significant percentage of the players receiving 'PED' suspensions since the new CBA took effect would not have been suspended. Instead, these players, under the proposed new policy, would have been subjected to the Substance Abuse Policy and Program.
"More than 80 missed games, millions of dollars in fines and bonus repayments have been issued because the NFLPA and NFL cannot come to an agreement. The only people who are losing in this standoff are the players and fans."
The last known Cowboys player to be suspended for violation of the NFL's substance abuse policy was defensive back Marcus Coleman, who was released in October of the 2006 season after he served a four-game suspension and was arrested on suspicion of driving while intoxicated.
ESPN's Ed Werder and ESPNDallas.com's Calvin Watkins contributed to this report.