Using cannabis and opiates for pain medication together can have additive effects, which means that it will amplify the depression in the central nervous system (CNS). Since the CNS is responsible for controlling heart rate and respiration, too much depression from using both cannabis and opiates at the same time may actually lead to death. Because of this, it would be wise for patients to consult with doctors to reduce the dosage of opiates while medicating with cannabis. Read more here.