In the United States, the prohibition of marijuana arose in many states from 1906 and onward.  By the mid-1930s, marijuana was regulated in every state by laws instituted through The Uniform State Narcotic Act.  In the 1970s, many states in the United States started to decriminalize marijuana.  Most places that have decriminalized cannabis have one or more of civil fines, drug education, drug treatment for possession of small amounts of cannabis, or have made various cannabis offenses the lowest priority for law enforcement.  In the 1990s many places began to legalize medical cannabis, which conflicts with federal laws, as cannabis is a Schedule I drug according to the Controlled Substances Act of 1970.  This means that marijuana is treated as having high potential for abuse, no medical use, and is not safe to use under medical supervision.

The rules concerning marijuana vary in the different states of U.S.  The related law of each state is discussed under the following state links.