Major medical marijuana growers are changing their ways in Oregon after federal agents raided selected "monster grows" to send the message that the state law can't serve as cover for black market sales.

State figures obtained by The Associated Press show the number of gardens registered as serving multiple patients will be far fewer in 2012 - down 26 percent for those serving five patients or more, and down 36 percent for those serving 10 or more.

Last fall federal agents raided five large cooperative medical marijuana gardens in Jackson County.

The U.S. attorney for Oregon, Amanda Marshall, is not taking credit for the decline, but she says federal agents are keeping up the pressure. She says efforts are now focused on the growing number of medical marijuana dispensaries.