More than half of the states that have legalized recreational marijuana use have signed up for Colorado’s program.
The other states are New York, Massachusetts, Maine, Washington and Oregon.
Colorado has seen a steady rise in usage, with more than 7.5 million patients using the drug.
It’s now the fifth-most popular recreational drug in the United States.
A Gallup poll released this week found that nearly four-in-ten Americans say marijuana should be legal for recreational and medical use.
A majority of Americans (53%) now favor legalizing recreational marijuana for medicinal use.
Associated Press writer Michael Biesecker contributed to this report from Denver.