U.S. states that have legalized the use of cannabis for medical treatments. 1. Maine is one of the almost two dozen U.S. states that have legalized the use of cannabis for medical treatments. 2. The medical cannabis law in Maine was approved on November 2, 1999, after receiving 61% of the votes. It was made effective on December 22, 1999. It allows qualified people to use, possess, and grow cannabis. 3. In order to be qualified to use, possess, and grow cannabis in Maine, one has to ...