The Canadian Government hasn't been able to stamp out the black market by legalising cannabis there.

The drug has been legal there for around a year.

Canadian Centre on Substance Abuse and Addiction director Rebecca Jesseman told Mike Hosking people who have established dealers are not going to switch to the legal market overnight.

"We had a lot of difficulties with consistency of supply during the first year, the market is definitely still stabilising. It probably will take a few more years yet to do so."

The law also hasn't stopped underage people using it.

Under the government's draft cannabis bill announced by Justice Minister Andrew Little, people wouldn't be able to use or buy or use cannabis until they're 20.

In Canada, the age of purchase is 19.

Jesseman says young people haven't stopped consuming cannabis but there also hasn't been an increase.

"We already knew that a very large number of youth in Canada were consuming cannabis pre-legalisation, so there was a lot of concern that that would increase even higher."