The U.S. government will intervene in a whistleblower case against Insys Therapeutics over sales and marketing tactics meant to induce doctors to prescribe a powerful opioid.

Documents unsealed May 14 revealed that the Department of Justice is pursuing action under the False Claims Act and the anti-kickback statute against Insys for encouraging physicians to prescribe the opioid, Subsys, when it was unnecessary. The DOJ said Insys misrepresented diagnoses in order to be reimbursed by Medicare.

Opioids, including prescription medications, are blamed for more than 42,000 deaths in the U.S. in 2016 alone, according to the U.S. Centers for Disease Control...