New York, April 25 (IANS): A medication commonly taken for Type-2 diabetes, which also finds its way to freshwater systems worldwide, is causing intersex in fish - male fish that produce eggs, says a study.

Exposure to the diabetes medicine metformin causes physical changes in male fish, the findings showed.

Because intersex fish are particularly prevalent downstream from wastewater treatment plants, many studies have investigated the effect of hormones from birth control pills, said Rebecca Klaper from the University of Wisconsin-Milwaukee in the US.

Initially, the results of her study seemed surprising since metformin is not a hormone and it targets blood sugar regulation.

But Klaper said it is also prescribed to women with a common hormonal disease called polycystic ovary syndrome.

The research in her lab indicates metformin could be a potential endocrine disruptor -- a chemical that confuses the body's complicated hormonal messaging system, interrupting a range of normal activities, including reproduction.

Of the chemicals she has detected in water samples collected from Lake Michigan, metformin stands out, Klaper said.

"It is the chemical we found in almost every sample and in the highest concentrations compared to other emerging contaminants - even higher than caffeine," she said.

For the study, the researchers monitored fish that had continuous exposure to metformin from birth to adulthood.

The study was published in the journal Chemosphere.