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Within months of launching a registry to prevent patients from receiving opioids and other potentially addictive prescription drugs from more than one doctor, Pennsylvania saw a substantial drop in the number of prescriptions for painkillers such as Vicodin, OxyContin and Percocet.

Authorized by the state legislature in 2014, Pennsylvania’s prescription drug monitoring program began operation only in June because of budget constraints. Within months, insurers reported a decline in total opioid prescriptions.

Pennsylvania’s online registry allows prescribing nurses and physicians to see which prescriptions a patient may already be receiving. Similar to other states, Pennsylvania requires pharmacists to update patients’ drug history each time they fill a prescription.

In the first eight months of 2016, Highmark, one of Pennsylvania’s largest insurers, said the number of monthly reimbursements for opioid painkillers ranged from 110,000 to 118,000. From September through November, the number was about 107,000 each month. Other insurers in the state also reported small declines.

Nationwide, the number of prescriptions for highly addictive opioid painkillers dropped 10 percent between 2013 and 2015, a decline attributed to greater awareness of the dangers of painkillers as well as to more-restrictive federal guidelines and state drug monitoring systems.

Overdose deaths involving prescription opioid painkillers have quadrupled since 1999, as have sales of the drugs. From 1999 to 2015, more than 183,000 people died in the United States of overdoses related to prescription opioids. In 2015, prescription opioids were involved in more than 33,000 deaths, the Centers for Disease Control and Prevention reported.