PROVIDENCE — It has been two years since Rhode Island launched its medical marijuana market and opened dispensaries around the state, but tax revenues haven’t been quite as high as state officials expected.

There are now three medical marijuana dispensaries — also known as compassion centers — selling marijuana to patients in Rhode Island, with the state collecting a 4 percent surcharge and a 7 percent sales tax on all their transactions. While revenues are increasing, some centers say they’re facing increasing competition from caregivers who can grow and sell medical marijuana without paying taxes to the state.

‘‘There are people out there who’ve made this a full-time business,’’ said Chris Reilly, a spokesman for the Thomas C. Slater Compassion Center in Providence. ‘‘It’s a competitive force that’s real.’’

State officials report that medical marijuana revenues are about half of what was predicted as the state prepared to legalize compassion centers. The dispensaries don’t have to disclose sales figures, but the state discloses aggregate figures for the revenues it collects. [Read more from the Associated Press at the Boston Globe]