It’s a common problem.

Your doctor prescribes medicine, you don’t use it all and don’t know what to do with the extra. What you don’t want to do is keep them.

To make it easier to get rid of leftover prescription drugs, CVS Health and Walgreens are installing machines for disposal in their drugstores. Consumers simply drop the unwanted medication into what looks like a mailbox.

Drug disposal programs are one way to help stem the growing opioid crisis. It may seem harmless to save leftover pain pills for a rainy day, but kids and teens can get into them. Worse, their experimentation can lead to addiction.

So many people are overdosing from heroin and synthetic opioids that the U.S. life expectancy shortened two years in a row. The Surgeon General recently urged more people to carry opioid antidote naloxone, the first advisory from a surgeon general since 2005.

The drug supply chain has come under scrutiny for its role in fueling the crisis. States and local governments have sued drugmakers and distributors, and the Trump administration has indicated it will get involved.

Pharmacies weren’t allowed to take back prescriptions until 2014 when the Drug Enforcement Administration issued new regulations in response to the growing opioid epidemic. Before then, people could typically only dispose of them at police departments. Some people weren’t comfortable dropping them off at police stations or just didn’t know they were there.

“We know firsthand patients are looking for solutions,” said Rick Gates, Walgreens’ senior vice president of pharmacy operations. “We asked patients, and what we heard was bringing medications back to pharmacies felt like the right thing to do because they’re the places they go to pick up their prescriptions.”

Walgreens started adding drug disposal units in 2016 and now has 600. It’s collected 155 tons of medications since the program began. AmerisourceBergen, the Blue Cross Blue Shield Association, Pfizer and Prime Therapeutics are partnering with Walgreens to add kiosks to another 900 stores.

Stericycle, a company specializing in disposing of regulated substances like pharmaceuticals and medical supplies, removes the drugs and incinerates them. They had initially planned on emptying the kiosks once a month, but they were filling up so quickly they had to clear them once a week or once every other week in some cases, Gates said.

“We’re quite excited by what we’ve done. Obviously our goal with experience is to continue to drive that story up about unused medications in cabinets and how do we prevent abuse,” he said.

CVS Health is in the process of installing 750 kiosks to its stores. It’s already donated more than 800 units to police departments. By June, it will have more than 1,600 in total.

Installing each unit takes time and planning to make sure it complies with regulations, said Tom Davis, CVS Health’s vice president of pharmacy professional services. They must be bolted into the floor so people can’t them pick up, they need to be locked at all times, and when they’re emptied and sent to a disposal company they must comply with the DEA’s protocols, among other requirements, he said.

“(Installing a kiosk) sounds like an easy thing to do, but when you think about all the regulatory complexity, you gotta get it right and do each one at a time,” he said.

Permanent kiosks are still only available at a fraction of pharmacies around the country, but there are other alternatives for people looking to get rid of medications. Police departments, fire stations and some local government buildings offer them.

On April 28, the DEA will sponsor its semi-annual National Prescription Drug Take Back Day when people can bring their leftover prescription drugs to police departments, drugstores and other collection sites.

Walmart gives pharmacy customers powder called Dispose Rx that turns solid when mixed into a pill bottle with warm water, making it safe to throw it away. Rite Aid sells envelopes people can use to return their extra medications.

Some medicines are safe to flush down the toilet, according to the Food and Drug Administration. For others, the agency recommends removing them from their original containers and mixing them with something undesirable like cat litter or coffee grounds then putting them in a container like a plastic bag and throwing them away.