Yes, it is illegal to possess *marijuana* for any reason except in 14 states (AK, CA, CO, HI, ME, MI, MT, NV, NJ, OR, RI, VT, WA) where it has been legalized for medicinal use. So in a way it is legal although the federal government can somehow violate the constitution and come in and charge you with federal crimes even though your state may have made it legal. Will it ever be legal, legal, like alcohol or tobacco, hopefully someday. One issue of the marijuana debate is why is the nonintoxicating plant that hemp is derived from illegal? Well that issue delves into why marijuana is illegal in the first place.
Prior to 1920: As well as being used for centuries for medicinal and industrial uses, the United States Department of Agriculture issues Bulletin No. 404: Hemp Hurds as Paper-Making Material, printed on hemp paper, outlining a revolutionary new hemp pulp technology invented by USDA scientists Dewey Lyster and Jason Merrill.
The bulletin lists increased production capacity and superior quality among the advantages of using hemp for pulp. Lyster writes in Bulletin No. 404, Every tract of 10,000 acres which is devoted to hemp raising year by year is equivalent to a sustained pulp producing capacity of 40,500 acres of average wood-pulp lands. Hence, an acre of hemp produces four times as much pulp as an acre of trees.
At the same time hempseed oil was one of the primary heating sources for the United States and industrial hempseed oil has a multitude of uses: lubricants, paints, inks, fuel and plastics. Hempseed oil has found some limited use in the production of soaps, shampoos and detergents. The oil is of high nutritional value because its 3:1 ratio of omega-6 to omega-3 essential fatty acids, which matches the balance required by the human body.
1920 - 1940: Economic power in the United States begins to consolidate in the hands of a small number of steel, oil and munitions companies. DuPont becomes the U.S's primary manufacturer of munitions/chemicals. DuPont later creates Rayon, the world's first synthetic fiber, from stabilized guncotton. The overall usefulness and efficiency derived from the hemp plant (a completely different plant than that of the medicinal cannabis) threatens the leaders of industry especially Dow Chemical and many of the petroleum industrialists, here's what happens next:
1936 - 1938: William Randolph Hearst's newspaper empire fuels a tabloid journalism propaganda campaign against marijuana. Articles with headlines such as Marihuana Makes Fiends of Boys in 30 Days; Hasheesh Goads Users to Blood-Lust create terror of the killer weed from Mexico.
1937: The year the federal government outlawed cannabis. DuPont patents petrochemical manufacturing processes for making plastics, as well as pollution-heavy sulfate/sulfite processes for producing wood pulp. For the next 50 years, these processes are responsible for 80% of DuPont's industrial output.
April 14, 1937: The Treasury Department secretly introduces its marijuana tax bill through the House Ways and Means Committee, bypassing more appropriate venues. Committee chairman Robert L. Doughton, a key Congressional ally of DuPont, rubber-stamps the bill.
December 1937: The Marijuana Tax Act is signed into law, initiating 60+ years of cannabis prohibition and annihilating a multi-billion dollar industry. DuPont and other synthetic materials manufacturers reap vast profits by filling the void conveniently left by the criminalization of industrial hemp.
February 1938: Popular Mechanics describes hemp as the new billion dollar crop. The article was actually written in the spring of 1937, before cannabis was criminalized. Also in February 1938, Mechanical Engineering calls hemp the most profitable and desirable crop that can be grown.
1941: Popular Mechanics introduces Henry Ford's plastic car, manufactured from and fueled by cannabis. Hoping to free his company from the grasp of the petroleum industry, Ford illegally grew cannabis for years after the federal ban.
1942: The Japanese invasion of the Philippines cuts off the U.S. supply of Manila hemp. The U.S. government immediately distributes 400,000 pounds of cannabis seeds to farmers from Wisconsin to Kentucky.
Just four short years after cannabis was outlawed as the assassin of youth, the government requires farmers to attend showings of the USDA pro-cannabis classic, Hemp for Victory.
1989: A government-funded study at the St. Louis Medical University determines that the human brain has receptor sites for THC to which no other known compounds will bind.
December 30, 1989: Ignoring evidence to the contrary, Drug Enforcement Agency Director John Lawn orders that cannabis remain on the Schedule One narcotics list, reserved for drugs which have no known medical use.
2006: The report, "Marijuana Production in the United States," by marijuana policy researcher Jon Gettman, concludes that despite massive eradication efforts and monetary cost at the hands of the federal government, "marijuana has become a pervasive and ineradicable part of the national economy." the report cites marijuana as the top cash crop in 12 states and among the top three cash crops in 30.
The study estimates that marijuana production, at a value of $35.8 billion, exceeds the combined value of corn ($23.3 billion) and wheat ($7.5 billion).
So there you have it, so long as it helps turn a profit the U.S. will go along with corporations over the benefit and well being of its citizens.