The chairman of a commission set up to oversee the implementation of a medical marijuana program told lawmakers Thursday that the initiative is at least 18 months away from offering pain relief to the first patients.

Even with that much time, it is by no means certain that the program will get off the ground, said Dr. Paul W. Davies, a pain relief specialist who heads the Natalie M. LaPrade Medical Marijuana Commission. The panel is charged with writing the rules for the program, which limits the program to five academic medical centers.

Davies told the House's marijuana work group that even under the best-case scenario it would take 1 1/2 to 2 years after July 1 for a medical center to set up a program and to make an arrangement for a grower to provide the marijuana.

So far, he said, the state's academic medical centers have been wary about participating in the program, which was authorized by the legislature last year as Maryland's first, tentative step toward permitting the use of marijuana to alleviate medical conditions. He said the centers receive federal grants and are apprehensive they could be jeopardized in the institutions participate.

Davies spoke after lawmakers heard a presentation from Mary Lynn McPherson, a professor at the University of Maryland School of Pharmacy who specializes in pain medicine. McPherson said marijuana is effective in treating pain and decreasing the need for opiate drugs in a significant number of patients. She also said marijuana has not been shown to be a "gateway" to other drugs.