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Anxiety drugs that end up in water are making fish risk-takers, as they have started becoming detached from their schools and eating all the food around them, according to a latest study.

Researchers from Umeå University found that fish started behaving differently when they were exposed to Oxazepam, a mood altering drug, in concentrations found normally in areas in Sweden that are densely populated.

The study team assessed the drug's concentration in the Fyris River, in Sweden, which passes through some very densely populated areas. The team found that perch (Perca fluviatilis) had at least 6 times more drugs in their body than the surrounding water, Nature reports.

Staying in groups or schools is good for the fish as it makes foraging easier and less risky. However, the anxiety drug is changing this behavior, making the fish isolated and risk-takers that go away from the schools on their own.

"Normally, perch are shy and hunt in schools. This is a known strategy for survival and growth. But those who swim in Oxazepam became considerably bolder," said ecologist Tomas Brodin, lead author of the article.

These fish on the anxiety drug were also more likely to eat more food. The food chain in nature is a delicate balance of energy exchange, and so fish eating more food causes serious disruptions in the ecosystem.

"We're now going to examine what consequences this might have. In waters where fish begin to eat more efficiently, this can affect the composition of species, for example, and ultimately lead to unexpected effects, such as increased risk of algal blooming," says Brodin.

Oxazepam isn't the only drug that's changing fish behavior. Recent studies have shown that birth control pills are wreaking the sex life of fish by making the male fish less masculine and creating a condition called as intersex.

Removing the drug from the sewage waters may be a way to deal with the problem.

"The solution to the problem is not to stop medicating ill people but to try to develop sewage treatment plants that can capture environmentally hazardous drugs," said Jerker Fick, environmental chemist.

The study is published in a recent edition of Science.