Colorado became the first U.S. state to regulate and tax sales of recreational marijuana yesterday, the Denver Post reports. Legislators levied a 15 percent excise tax, and a 10 percent sales tax on cannabis in order to pay for enforcing regulations like capping marijuana sales to Colorado visitors at a quarter of an ounce, a six-plant limit on pot gardens, mandatory child-resistant packaging, potency information and serving-size limits for edible marijuana. How grown-up!