Let's first differentiate two actions states have taken with respect to marijuana. Decriminalization refers to the relaxation of criminal penalties associated with personal marijuana use. Oregon was the first state to decriminalize marijuana in 1973. The state imposed just a $100 fine for possession of up to an ounce.
Over the next 15 years following Oregon's legal change, at least a dozen other states decriminalized marijuana. But decriminalization merely lowered or removed the sting from anti-marijuana laws. Manufacturing and selling marijuana remained illegal.
Legalization, on the other hand, not only allows individual marijuana possession, but in most cases it also permits the legal production and sale of the drug. There are two types of marijuana legalization: the legalization of medical cannabis and the legalization of recreational marijuana.
All but four U.S. states have some form of medical marijuana law. However, 16 states only allow legal use of cannabidiol (CBD) or medical cannabis that has a low tetrahydrocannabinol (THC) content. CBD is a chemical ingredient of the cannabis plant that isn't psychoactive, while THC is the primary psychoactive ingredient in cannabis. These 16 states usually aren't included in the number of states that have legalized medical marijuana, because their laws place strict limitations on the form and manner of medical marijuana use. Thirty states, however, allow broad access to marijuana for medical purposes for patients.