Cannabis in South Dakota is illegal for all purposes, and possession of any amount is a criminal offense. South Dakota is the only U.S. state which outlaws ingestion of controlled substances. Testing positive for cannabis can be a misdemeanor offense.
As part of a larger trend nationwide to restrict cannabis, South Dakota banned the drug in 1931.
Decriminalization and repeal (1977)
In 1977, during a short-lived wave of decriminalization in the country, South Dakota decriminalized cannabis, but repealed that law "almost immediately" afterward.
Medical cannabis attempts (2006–2015)
Ballot initiatives to legalize medical marijuana appeared on the 2006 and 2010 election ballots in South Dakota, but failed both times. The 2006 initiative lost 52%-47%, while the 2010 initiative lost 63%-36%. Cannabis activist Emmett Reistroffer commented that the decrease of support in 2010 was due in part to the rise of the Tea Party movement and the presence of an anti-cigarette smoking bill on the same ballot.
In mid-2015, there was an effort to place yet another ballot initiative on the 2016 election to legalize medical marijuana, but unlike in 2006 and 2010, the Marijuana Policy Project did not anticipate financially supporting the initiative due to strong cannabis campaigns in other states requiring attention for that election.
In mid-2015, South Dakotans Against Prohibition began circulating petitions to put decriminalization of marijuana on the November 2016 ballot, reclassifying possession of one ounce (28 g) or less a civil, rather than criminal, infraction, and remove penalties for paraphernalia and consumption. However, SDAP failed to gather the 13,871 signatures necessary to place an initiated measure on the ballot and stated it would withdraw its petition.
2018 medical cannabis ballot initiative
In November 2017, activists turned in over 15,000 signatures, narrowly meeting valid signature requirements, in order to place medical cannabis on the 2018 ballot. The initiative failed to make the ballot due to an insufficient number of valid signatures. 
2020 cannabis ballot initiative
South Dakota Initiated Measure 26 was certified by the South Dakota Secretary of State for the 2020 ballot on December 19, 2019. If passed, this would establish the use of medical marijuana in the state.
A vote on South Dakota Constitutional Amendment A will also be held in 2020, which would legalize the use of recreational marijuana in South Dakota.
Recreational legalization on the Flandreau Santee Sioux Tribe reservation
In mid-2015, the Flandreau Santee Sioux Tribe, located in eastern South Dakota, stated their intent to begin growing cannabis on one authorized site on their reservation, and commence selling the product on 1 January 2016, following a vote of tribal authorities which decided 5–1 to legalize cannabis. Facing legal uncertainties, the tribe destroyed millions of dollars worth of marijuana on November 7, 2015.
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