The number of people authorized to possess marijuana under the federal program has risen to 37,000 this year from fewer than 100 in 2001.
In a court document defending planned changes to the program, the government says growing marijuana at home poses hazards including mould, fire, toxic chemicals and the threat of home invasion by criminals.
It says the number of licensed users could climb as high as 400,000, adding it is not possible for Health Canada to effectively inspect tens of thousands of production sites across the country.
Under the existing program, to be eliminated April 1, people are issued licences to grow marijuana for their personal use to help ease painful symptoms.
Several British Columbia residents are asking the Federal Court of Canada for an injunction that would allow them to continue producing their own pot.