New rules for the medical marijuana program in Colorado are under consideration by the state Board of Health. The board is looking at new rules to limit high-volume caregivers. Those are people authorized by the state to grow marijuana on behalf of others, and they’re not subject to state taxes or background checks. The board is also looking at setting guidelines for marijuana-related research grants awarded by the Health Department. The board didn’t make any decisions on the changes yesterday. Instead, the board will take public comment and decide whether to hold a hearing in September on the proposed rules.