Marijuana would be taxed and regulated like alcohol under a bill being backed by more than a dozen Massachusetts lawmakers.

The bill would let adults 21 years or older to possess and grow limited amounts of marijuana.

The proposal would also create a regulated system of licensed marijuana retail stores, cultivation facilities, processing facilities and testing facilities.

Support for GBH is provided by:

The bill is being pushed by the Marijuana Policy Project. The group says it plans to put a question on the 2016 ballot to regulate and tax marijuana if the bill fails to win support on Beacon Hill.

The bill is sponsored by two Democrats — Rep. David Rogers of Belmont and Sen. Pat Jehlen of Somerville. It’s co-sponsored by 13 other lawmakers.

Voters have already approved two previous pro-marijuana ballot questions.