Story highlights Libertarian nominee Gary Johnson said he did not agree with Mitt Romney that "marijuana makes people stupid"

Johnson said he thinks legalizing marijuana could lead to less overall substance abuse

Watch Erin Burnett's exclusive interview with Gary Johnson on CNN International Sunday at 10 a.m. and 8:30 p.m. ET.

Washington (CNN) Libertarian presidential hopeful Gary Johnson is sticking up for marijuana after 2012 GOP nominee Mitt Romney last week said smoking the drug "makes people stupid."

"I do not agree with that," Johnson told CNN's Erin Burnett in an interview scheduled to air Sunday on "OutFront." "As someone who has used marijuana, I do not agree with that."

Johnson, who was the governor of New Mexico from 1994-2003, has been an advocate for legalizing marijuana since 1999 . In his interview with Burnett, he suggested that marijuana "competes with legal prescription painkillers and drugs that statistically kill 100,000 people a year."

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He noted that there has not been one documented death due to medical marijuana.

"On the recreational side, I have always maintained that legalizing marijuana will lead to overall less substance abuse because it's so much safer than everything else that's out there starting with alcohol," Johnson said.

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