DENVER (AP) -- A voter-approved marijuana legalization amendment in Colorado was declared part of the state constitution Monday by Gov. John Hickenlooper.

Hickenlooper's declaration, a procedural step, means that marijuana is effectively legal for recreational use in Colorado. The drug became legal in Washington state last week.

Hickenlooper tweeted his declaration and announced it to reporters by email. The Democratic governor said voters were "loud on clear" when they voted last month to make pot legal without a doctor's recommendation. Adults over 21 may now possess up to an ounce of marijuana, or six plants.

Colorado and Washington officials both have asked the U.S. Department of Justice for guidance on the laws that conflict with federal drug law. Neither state will allow commercial sales for a year or more.