Adults 21 and older who are Illinois residents will be allowed to possess and use up to 30 grams of cannabis flower, 5 grams of concentrate, and 500 milligrams of THC in a cannabis-infused product like candy or brownies. Non-Illinois residents may possess up to half that much. Pot will remain illegal for those younger than 21, and it will remain illegal to drive while impaired — though there is no scientifically established measure of impairment, and no court-approved breath or saliva test.