Blackmon previously was suspended for the first four games of this season for violating the policy.
His latest suspension begins immediately. He will be eligible to apply for reinstatement prior to the start of the 2014 season.
"I want to sincerely apologize to Mr. (Shad) Khan, my teammates, my coaches and to the Jaguars fans for not utilizing the resources that I was provided to overcome my challenges," Blackmon said in a statement released by his agent. "I am determined to overcome the issues that have resulted in this situation, and I truly appreciate the support that the Jaguars and my agent have shown me.
"I will address these matters with the type of intensity I usually direct toward my on-field play so that I can be ready to be a productive member of the team and community next season. Again, I am truly sorry to Mr. Khan, my teammates and coaches and to the Jaguars fans for the impact of my situation on the team as well as to my family and friends and those that have been there for me during these challenging times. Nobody is more disappointed with all of this than me."
Jaguars general manager David Caldwell addressed Blackmon's situation.
"All of us who are a part of the Jaguars family care very deeply about Justin and his well-being," Caldwell said. "That said, he must be held accountable and accept the consequences announced today by the NFL.
"His suspension will provide him the opportunity to receive the attention and professional treatment necessary to overcome his challenges, and we will support him during this time. The Jacksonville Jaguars will evaluate Justin's status once he has successfully met the criteria to be considered for reinstatement to the league."
Caldwell added he hopes Blackmon will play for the Jaguars again but that's a secondary concern after the receiver's health.
Blackmon has registered 29 catches for 415 yards and a touchdown for the winless Jaguars (0-8), who have a bye this week.
Selected fifth overall in 2012, Blackmon caught 64 passes for 865 yards and five touchdowns as a rookie.
Blackmon's past troubles have been well documented. He was arrested on a misdemeanor DUI charge in Texas in 2010 after officers caught him speeding on a suburban Dallas highway. The charge was later reduced to an underage alcohol possession charge. A little more than a month after the Jaguars traded up to select the former Oklahoma State star in the draft, he was arrested during a traffic stop in Stillwater, Okla., after a breath test allegedly showed his blood alcohol content to be three times the legal limit.
That arrest landed him in the NFL's substance-abuse program.
Information from ESPN.com Jaguars reporter Mike DiRocco and The Associated Press was used in this report.