A US drug investigator is pushing back against claims legalised cannabis is a good thing.

Colorado Drug Investigators Association president Ray Padilla told Mike Hosking since legalising cannabis, the societal issues they're dealing with have shot up.

He claims deaths from people driving after taking marijuana in the state have increased by 151 percent.

Padilla says emergency room numbers and poison cases are sky-rocketing.

"Definitely an increase in visit due to a lot of different things. A lot of psychotic issues, a lot of mental issues, our rehab clinic, there is rehab for marijuana, so you can get addicted to it."

He says there's more organised crime than ever before in Colorado.

"When you can get it on the black market, number one its much cheaper. Number two, you are going to have gangs and those here who are going to grow it here in Colorado and then ship it out of state."

Padilla says marijuana is worth up to $1,200 a pound in Colorado, whereas on the East Coast, gangs can get up to $7,000.

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