The popular antidepressant drug Prozac inhibits sexual activity in fish by interfering with sperm production and pheromone transmission, which raises environmental concerns, according to a study by University of Ottawa researchers.

The study, published in the Aquatic Toxicology journal on Tuesday, found that male goldfish exposed to water treated with Prozac experienced decreases in sperm production of up to 50 per cent. They also reacted less to the pheromones released by female fish.

The researchers tested fish in two grades of treated water for week-long periods. The first type of water had a low level of Prozac content, equal to that found in sewage effluent, while the other had a much higher concentration. Both levels produced lower levels of sperm and pheromone reaction.

The lower level, according to professor Vance Trudeau, is environmentally relevant because it's what humans produce when they urinate the unprocessed parts of the drug. Existing sewage plants, he said, are not designed to eliminate these trace elements.

"Even if they do degrade, which Prozac will … we're adding to it every time we flush," Trudeau said.

The findings mean that Prozac and drugs like it — selective serotonin reuptake inhibitors that use fluoxetine as their active ingredient — are environmental pollutants that can affect fish breeding levels in the wild, the researchers said.

Trudeau said that some countries, such as Germany, have taken a zero-tolerance approach to environmental pollution from pharmaceuticals. Sewage treatment plants in such places are investing in the expensive equipment required to filter drugs out of their sewage.

"We're a little bit sloppy in North America and we don't push our politicians enough," he said. "It can be done but right now it's expensive. That is the big challenge."

Prozac, which is taken by more than 54 million people worldwide, lists decreased sex drive in humans as one of its possible side-effects.

A spokesperson for Eli Lilly, the company that produces the medication, said she was not familiar with the University of Ottawa study but that environmental concerns are a priority.

"We and the whole pharmaceutical industry work to ensure that the manufacture, distribution, use and disposal of our products are conducted in an environmentally safe manner," said Sonja Popp-Stahly. "Patient and environmental safety related to our products is a top priority for us and the industry."