Law enforcement officials report an increase in cases of people are stealing items from major retailers, returning them for gift cards, and cashing in the cards to pay for opioids, CNBC reports.

People steal items and return them to another store without a receipt, and receive a gift card in return. They sell the gift card to a pawn shop or secondary store at a discount. The cards are then resold to an online exchange.

In Knox County, Tennessee, police found 16 of 19 drug overdoses were linked to the sale of gift cards during a one-month period this year. In the city of Knoxville, police linked almost 100 overdoses to gift cards during a three-month period.