Colorado became the first US state to legalize marijuana for adults over the age of 21 in 2012, followed by nine other states — including California and Massachusetts — by the beginning of 2018.
On top of that, another 30 states have some form of medical marijuana laws on the books, including Oklahoma, one of the most conservative states in the US.
Neither Congress nor President Donald Trump's administration have legalized marijuana at the federal level (though there are a number of bills circulating around the House and Senate), so some questions still remain over whether the US will legalize marijuana outright.
While multiple states have set up successful markets for recreational marijuana, Muggah said that some policies lack proper consideration for communities who were hurt most by drug prohibition.
"While there have been important advances on the public health front, states and cities across the US are still lagging when it comes to criminal justice reform," Muggah said.