The US State of Colorado is continuing to fight the cannabis black market, six years after legalising the drug.

Seizures of marijuana in the U.S mail system have increased more than 1000 per cent since 2013, as Colorado becomes a major exporter of the drug.

National Drug and Alcohol Screening Association executive director, Jo McGuire, told Kate Hawkesby greater rules and regulations are needed.

"Not only do people completely bypass the regulatory system when they are a player, but people from other countries [are] flooding our state and setting up illegal grow operations in our national forest."

She said legalisation is not the solution to drug reform.

"We just had a study released which said that we are actually spending US$4.50 for every dollar that we bring in on taxes. We are seeing one in four employees self report that they go to work stoned."