Nearly 15 million Americans admit to driving high in the last month

Medical marijuana is legal in Florida but you can still be charged with driving under the influence. The survey shows 70% of Americans believe — mistakenly — that is unlikely.

Tampa Police Department Officer Roy Paz explained how they spot high drivers.

"They're going to have slower reaction times, limited short-term memory," Paz said. "They're going to have decreased hand and eye coordination. We do those types of tests there on the scene just like we would for a regular alcohol stop."

But Tampa attorney Michael Minardi, who has dedicated his practice to defending those accused of cannabis crimes says, it's not easily detected.

"We do need more technology, so they do not have necessarily roadside exercises and things like that to be able to discover impairment on the roadsides," Minardi said.

According to the National Highway Traffic Safety Administration, between 2007 and 2014, there was a 48% increase in weekend nighttime drivers testing positive for THC, the main active ingredient in cannabis.

Minardi says more focus needs to be put on responsible use.

"And that's the bottom line with any substance, with any use. Whether it be cannabis, or alcohol, or anything," Minardi said.