Canada's Prime Minister Justin Trudeau, who spoke on the eve of the reform, said: "We're not legalizing cannabis because we think it's good for our health. We're doing it because we know it's not good for our children.
A marijuana prohibition that has lasted close to 100 years in Canada ended on Wednesday following the country's legalisation of the drug for recreational use.
Canada became the first major Western nation to legalise and regulate its sale and recreational use.
Canada's Prime Minister Justin Trudeau, who spoke on the eve of the reform, said: "We're not legalizing cannabis because we think it's good for our health. We're doing it because we know it's not good for our children.
"We know we need to do a better job to protect our children and to eliminate or massively reduce the profits that go to organized crime."
Under the new regulations, Canadians aged at least 18 or 19 will be allowed to buy up to 30 grams of cannabis, and grow up to four plants at home.
Announcing the legalisation on Wednesday via his Twitter handle, Trudeau wrote: "Profits out of the hands of criminals. Protection for our kids. Today #cannabis is legalized and regulated across Canada."