Prozac Making Its Way Into Oceans Might Be Affecting Crab Behavior

A new study conducted in the Pacific Northwest examines how drugs are making their way into the ecosystem, affecting animals like the yellow shore crab (Hemigrapsus oregonensis). Alison Leigh Lilly/Flickr/CC BY-NC 2.0

Forty years have gone by since the debut of the popular antidepressant fluoxetine — popularly known by the trade name Prozac. After all this time, it's still the most effective and popular antidepressant on the market, and experts say it's not getting replaced anytime soon. And since demand for the drug is rising each year, it looks like more fluoxetine will be in our medicine cabinets. And as a result, that means we'll have more fluoxetine in our environment. And researchers want to know what it's doing.

It's not news that we ingest all kinds of chemicals — oral contraceptives, antibiotics, mood enhancers, and even caffeine — that end up in our toilets since our bodies can't entirely metabolize them. And after they're flushed, chemicals like fluoxetine end up in rivers and streams — and after that, in the oceans. What effect these chemicals have on ecosystems once they show up isn't well understood, but one 2016 study found that even small doses of the drug can render the notoriously aggressive Siamese fighting fish (Betta splendens) uncharacteristically chill.

A new study published in the journal Ecology and Evolution examines the effect of fluoxetine on shore crabs (Hemigrapsus oregonensis) on the Oregon coast, and finds exposure to the drug might be making them careless in their foraging habits.

A Portland State University research team exposed shore crabs in a lab to trace amounts of fluoxetine (at levels that have been detected on the Oregon shore) over the course of 60 days. They found these crabs foraged more during times of day they typically stay hidden, exposing them to the threat of predation. These crabs also fought more with others in their species — sometimes killing or being killed in the process.

"The changes we observed in their behaviors may mean that crabs living in harbors and estuaries contaminated with fluoxetine are at greater risk of predation and mortality," said researcher Elise Granek, a professor in Portland State University's department of Environmental Sciences and Management, in a press release.