United States jurisdictions with regulations for legalized recreational cannabis in effect before 2019
| Jurisdiction | Date legalization in effect | First month legalization in effect for primary analysis* | Date commercial dispensaries open | First month commercial dispensaries open for sensitivity analysis* | Cannabis-specific impaired driving law6 |
|---|---|---|---|---|---|
| Alaska7,8 | Feb. 24, 2015 | March 2015 | Oct. 29, 2016 | November 2016 | None |
| California9,10 | Nov. 9, 2016 | November 2016 | Jan. 1, 2018 | January 2018 | None |
| Colorado11,12 | Dec. 10, 2012 | December 2012 | Jan. 1, 2014 | January 2014 | Reasonable inference for impairment ≥ 5 ng/mL THC† |
| District of Columbia13 | Feb. 26, 2015 | March 2015 | No commercial | NA | None |
| Maine14,15 | Jan. 30, 2017 | February 2017 | Oct. 9, 2020 | NA | None |
| Massachusetts16,17 | Dec. 15, 2016 | December 2016 | Nov. 20, 2018 | December 2018 | None |
| Michigan18–20 | Dec. 6, 2018 | December 2018 | Dec. 1, 2019‡ | NA | Zero tolerance (no detectable presence of cannabis permitted) |
| Nevada21,22 | Jan. 1, 2017 | January 2017 | July 1, 2017 | July 2017 | Per se limit ≥ 2 ng/mL THC§ |
| Oregon23–25 | July 1, 2015 | July 2015 | Oct. 1, 2015¶ | October 2015 | None |
| Vermont26 | July 1, 2018 | July 2018 | No commercial dispensaries | NA | None |
| Washington27,28 | Dec. 6, 2012 | December 2012 | July 8, 2014 | July 2014 | Per se limit ≥ 5 ng/mL THC§ |
Note: NA = no data available for legalized (or commercial dispensaries open) months before 2019, THC = tetrahydrocannabinol.
↵* Rounded up or down to the nearest full month of legalization (or commercial dispensaries opening, for sensitivity analysis).
↵† Reasonable inference requires that the jurisdiction must prove with other evidence, in addition to exceeding the legal THC limit, that the driver was impaired.
↵‡ On Dec. 1, 2019, existing medical cannabis dispensaries in Michigan were permitted to transfer up to 50% of their medical cannabis inventory to recreational cannabis inventory. Until November 2021, retailers must hold a medical cannabis licence in order to apply for a recreational cannabis licence.
↵§ Per se limits do not require that the jurisdiction prove that drivers were impaired in order to charge them with driving under the influence if their THC level exceeded the legal limit.
↵¶ On Oct. 1, 2015, existing medical cannabis dispensaries in Oregon were permitted to sell recreational cannabis. The first licences were issued to recreational cannabis retailers on Oct. 1, 2016.