Massachusetts' largest health insurer is launching a policy to curb abuse by significantly limiting the amount of pain medication most patients can receive without prior approval from the insurer. The program by Blue Cross Blue Shield of Massachusetts, scheduled to start July 1, will allow patients to fill a 15-day prescription and one additional 15-day supply of the most common opioid drugs, such as Percocet and Vicodin, before the insurer hits the pause button. Future refills will trigger a Blue Cross review and the need for assurances from the prescriber that several requirements have been met, including patient counseling about the significant risk for developing an addiction.