Older men may have guns in the home that can pose a risk when people are depressed or not thinking clearly. iStockphoto.com hide caption

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Depression is common among old people, affecting up to 25 percent. iStockphoto.com hide caption

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Having a special someone won't fend off depression if that person doesn't have your back. iStockphoto.com hide caption

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Meredith Was, a senior at the University of Virginia, heads a chapter of the mental health advocacy group Active Minds. Jenny Gold for NPR hide caption

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Did eating binges come first? iStockphoto.com hide caption

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Among common health problems, depression was linked to the highest increase in annual spending by employers' on workers' health care. iStockphoto.com hide caption

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A rat neuron before (top) and after (bottom) ketamine treatment. The increased number of orange nodes are restored connections in the rat's brain. Ronald Duman/Yale University hide caption

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Chris Stephens, 28, who has been battling depression all of his life, plays with his dogs at home in Concord, Calif., on Friday. After a dose of ketamine, Stephens says, "I actually wanted to do things. I wanted to live life." Lianne Milton for NPR hide caption

itoggle caption Lianne Milton for NPR

Ketamine has been used as an anesthetic for decades. It's also a widely popular but illegal club drug known as "Special K." When administered in low doses, patients report a rapid reduction in depression symptoms. Huw Golledge/flickr hide caption

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