Marijuana—also known as marihuana or cannabis—is classified as a controlled substance under federal law, and its possession, use, and distribution is illegal. See 21 U.S.C. §812.

But many states have recently passed laws that generally legalize marijuana in some form. For example, Alaska, California, Colorado, Illinois, Maine, Massachusetts, Michigan, Nevada, Oregon, Vermont, and Washington have enacted laws legalizing marijuana for recreational use.

The District of Columbia allows all citizens over the age of 21 to possess up to two ounces of marijuana, to use and grow marijuana on private property, and to exchange marijuana between persons as long as no money, goods, or services are exchanged.

And some states that do not allow recreational use of marijuana do allow limited use of marijuana to treat symptoms of illness and other conditions—known as medical marijuana. States that allow limited use of medical marijuana include Arkansas, Arizona, Connecticut, Delaware, Florida, Hawaii, Louisiana, Maryland, Massachusetts, Minnesota, Missouri, Montana, New Hampshire, New Jersey, New Mexico, New York, North Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island, Utah, Vermont, and West Virginia. The medical marijuana laws in some of these states are broader than others, with some states only allowing use of cannabis-infused products such as oils and pills. Federal law prohibits health care practitioners from writing a prescription for medical marijuana, so practitioners in medical marijuana states write a recommendation for medical marijuana.

Other states have not legalized marijuana, but have decriminalized it—meaning possession of small amounts of marijuana is not punishable by jail or prison time, but may be punished with a fine. States that have decriminalized possession of marijuana under limited circumstances include Connecticut, Maryland, Mississippi, Nebraska, New Hampshire, New Mexico, New York, North Carolina, and Virginia.

Marijuana laws are generally located in a state’s statutes—often in the penal or criminal code, or in the health and safety code.

In Massachusetts, marijuana has been legalized for both recreational and medical use. Adults 21 years and older are allowed to possess, use, and grow marijuana within certain limits. Specifically, individuals can possess up to one ounce of marijuana on their person and up to ten ounces in their home. They can also grow up to six plants per person, with a maximum of 12 plants per household. The state has established a regulated market for cannabis, where licensed retailers can sell marijuana products. For medical use, Massachusetts permits qualifying patients to use marijuana for treatment of specific medical conditions. Patients with a written certification from a physician can obtain medical marijuana from state-licensed dispensaries. While Massachusetts state law permits the use and possession of marijuana, it remains illegal under federal law, which creates a complex legal landscape. However, federal enforcement of marijuana laws in states where it is legal has varied, with a general trend towards non-intervention in recent years.