Fish on Prozac Are Violent And Obsessive

Prozac is seeping out of sewage treatment plants and into rivers and lakes, turning male minnows into female murderers


Prozac’s host of side effects aren’t just limited to depressed humans. Fish, too, suffer when the drug washes into their streams, rivers and lakes. When people excrete Prozac’s active ingredient, fluoxetine, in their urine, the chemical finds paths into natural waterways through sewage treatment plants that are unequipped to filter it out. When male fish ingest the drug, it seemingly alters their minds to the point of dysfunction and even destruction. Nature News reports:

To investigate the effects of fluoxetine, researchers have turned to a common US freshwater fish species called the fathead minnow (Pimephales promelas). Normally, fathead minnows show a complex mating behaviour, with males building the nests that females visit to lay their eggs. Once the eggs are laid and fertilized, the males tend to them by cleaning away any fungus or dead eggs.

But when fluoxetine is added to the water, all of this changes.

Female fathead minnows seem to be unaffected by the chemical, but at concentrations of fluoxetine that are roughly comparable to the highest levels documented in fresh water, male minnows start to spend more time building their nests. When the dose is increased tenfold, the males “become obsessive, to the point they’re ignoring the females”, Klaper said

When fluoxetine reaches high enough concentrations, however, the males really lose it. They begin killing the females. Not surprisingly, any females that manage to escape the males’ murderous fins do not lay eggs.

As it turns out, a complex cascade of gene-expression changes and interactions are triggered when the drug enters the male minnow’s system. While understanding those pathways may help shed light on ways to combat the drug’s side effects in hapless male fish, weaning our Prozac nation off of the antidepressant would likely be the more surefire way of ensuring that the next generation of fathead minnows enter the world.

More from

Are Millennials Too Strung Out on Antidepressants to Even Know Who They Are?
Drugs’ Odd Side Effects

Get the latest stories in your inbox every weekday.