420: Time line

1914
The Harrison Narcotics Act makes it illegal to possess narcotics unless prescribed by a physician.

1937
The Federal Bureau of Narcotics begins to criminalize cannabis by passing the Marijuana Tax Act of 1937.

1956
Two to 10 years with a fine of up to $20,000 for first time cannabis possession offense.

1970
Cannabis is classified as having no medical use and being highly addictive.

1996
The Compassionate Use Act passes in California, legalizing medicinal use of marijuana in the state.

2005
The Supreme Court ruled that the federal government is within its right to regulate marijuana, medicinal and otherwise, under the commerce clause of the Constitution.

2009
The Obama administration signals that they will end raids on medical marijuana users who conform to the laws of their state.

2010
Alaska, Colorado, Hawaii, Maine, Michigan, Montana, Nevada, New Jersey, New Mexico, Oregon, Rhode Island, Vermont and Washington have legalized medicinal marijuana.