(CNN) -- After spending time indulging in the pleasures of Sin City, tourists heading back home may need to leave a thing or two behind -- like their weed.
The sale of recreational marijuana has been legal in Nevada since last summer , but pot is not legal at Las Vegas' McCarran International Airport.
So to keep travelers from getting in trouble in the airport security line, big green bins -- dubbed amnesty boxes -- were set up a week ago outside McCarran, allowing people to toss their pot before catching their flight. Twenty of the boxes were installed at McCarran and its car rental facility, Henderson Executive Airport and the North Las Vegas Airport.
The bins are about the size of a mailbox, bolted to the ground, monitored and designed to keep what's tossed in them inside the box. In addition to pot, the bins can also be used to drop off prescription drugs.
"We've had a variety of other things disposed of in the bins," Christine Crews, McCarran airport's public information administrator, told CNN. "For example, I was sent a picture of one of the bins containing pills, vape pens, rolled tobacco-looking products, prescription bottles and marijuana-infused drinks."
The boxes are periodically emptied by a contracted company that disposes of the contents.
The bins were necessary after Clark County, Nevada, which owns and operates the airport, banned marijuana possession and marijuana advertising on airport property last fall to stay in compliance with federal law.
Similar amnesty boxes were installed in airports in Colorado after that state legalized marijuana in 2012.
Nevada's marijuana law lets adults 21 and older possess up to an ounce of marijuana. Voters approved the law in November 2016.
Nine states and the District of Columbia now allow for recreational marijuana use , and 30 allow for medical use, but weed remains illegal under federal law.
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