An estimated 13 percent of Americans are currently taking prescription medication for depression, a 65 percent increase since the early 2000s. These drugs typically act as stimulants for neurotransmitters in the brain, which help regulate mood. While the effect is often beneficial for humans, scientists are beginning to learn it's having some unintended consequences for other species.

In a study recently published in Ecology and Evolution and covered by Newsweek, researchers at Portland State University took a closer look at how discarded antidepressants that wind up in inhabited waters impact marine life. The authors introduced fluoxetine, the main ingredient in Prozac, into a laboratory body of water inhabited by Oregon shore crabs, or Hemigrapsus oregonensis. Normally, the crabs are nocturnal foragers, avoiding confrontation and hiding in sediment when predators appear.

After being exposed to the drug, the crabs exhibited a dramatic change in behavior. Instead of shying away from predators—in the lab study, the larger red rock crab—they became more confrontational, increasing the risk of an early death. They also became more active during the day and displayed aggression towards other crabs, engaging in fights.

Drugs like fluoxetine end up in inhabited waters in a number of ways. Some people flush unwanted medication down the toilet, a measure that's even recommended by the FDA when users need to quickly dispose of dangerous drugs like OxyContin. Contamination from trash or human urine and stool can also be sources of pollution; a USGS study published earlier this year found antidepressants in the brains of fish living downstream from wastewater treatment plants. The study's authors warn that increased populations near coastal regions may worsen the issue. It's also unknown how concentrations of several different drugs can combine to alter behavior. Right now, it looks like our solution to one problem—depression—may have a host of ecological repercussions.

[h/t Newsweek]