Walmart is helping customers get rid of leftover opioids by giving them packets that turn the addictive painkillers into a useless gel.

The retail giant announced Wednesday that it will provide the packets free with opioid prescriptions filled at its 4,700 U.S. pharmacies.

The small packets, made by DisposeRX, contain a powder that is poured into prescription bottles. When mixed with warm water, the powder turns the pills into a biodegradable gel that can be thrown in the trash.

Research has shown that surgery patients often end up with leftover opioid painkillers and store the drugs improperly at home.

Walmart says the powder also works with other prescription drugs. The company says its pharmacy customers can request a free packet at any time.