Prescription drug monitoring databases are assisting states in battling the opioid epidemic, according to The Wall Street Journal.

A recent study found there was more than a 30 percent decrease in the rate of prescribing Schedule II opioids (such as Oxycontin and Percocet) in two dozen states with such monitoring programs.

Missouri is the only state that does not have a prescription monitoring database. The programs are used to prevent “doctor shopping”—patients who seek multiple prescriptions from different doctors. States are also using the databases to analyze doctors’ prescribing patterns. Some states allow law enforcement to access the information.