Health officials in Arizona say a small number of doctors have given the go-ahead for about 75 percent of medical marijuana cards issued in the state, raising questions about whether the program is being abused.

A report released Friday by the Arizona Department of Health Services said 24 doctors certified almost 75 percent of all cardholders from the inception of Arizona's medical marijuana program in April 2011 to June 2012. In all, 475 doctors certified nearly 29,000 patients in that period.