DENVER (AP) — Marijuana for recreational use became legal in Colorado Monday, when the governor took the procedural step of declaring the voter-approved change part of the state constitution.

Colorado became the second state after Washington to allow pot use without a doctor's recommendation. Both states prohibit public use of the drug, and commercial sales in Colorado and Washington won't be permitted until after regulations are written next year.

Hickenlooper, a Democrat, opposed the measure but had no veto power over the voter-approved amendment to the state constitution. He tweeted his declaration Monday and sent an executive order to reporters by email after the fact, preventing a public countdown to legalization as seen in Washington.