Thanks To Contraceptive Pill Waste, Male Fish Are Laying EGGS


Robin Andrews

Science & Policy Writer

This is a common roach, one of the types of fish exhibiting intersex features. Imageman/Shutterstock

There are certain things that you simply should never flush down the toilet. Plastic wrappers. Condoms. Beloved yet expired childhood pets. These things get stuck and cause several plumbing issues.

The toilet is not a magical waste disposal portal; it is not a wardrobe into a Narnia-like dumping ground. However, whether we mean to or not, a huge variety of stuff escapes into the wider world through them, and it can often have negative environmental consequences.


As some rather bizarre research by the University of Exeter has shown, contraceptive pills appear to be having a curious effect on certain wildlife too. It seems that because of the amount of related byproducts that are being released to the world below – along with numerous other chemicals and materials from other sources – at least one-fifth of all male fish in English rivers are now “intersex” in that they have both male and female physical characteristics.

Tests at 50 sites across England carried out by Exeter’s Professor Charles Tyler, a leading eco-toxicologist, confirmed the bizarrely high prevalence of intersex freshwater fish. Perhaps most curiously, some are even laying eggs.

Others have dramatically reduced sperm quantities, and are far less aggressive and competitive when it comes to getting mates. Consequently, they are less able to breed and produce offspring.

Intriguingly, the offspring of such fish are much more likely to be sensitive to the affecting chemical products than their non-contaminated compatriots are.

Contraceptive pills are one of just 200 chemical antagonists in this case. Image Point FR/Shutterstock

The most common contraceptive pill contains the female hormones estrogen and progesterone. Although it is not explicitly stated, it could be possible that an overload of these chemicals being released in the urine of those using them, or perhaps flushed down the toilet in pill form on some rare occasions, is what’s driving the so-called “feminization” of the freshwater fish. There are at least 200 other sewage-derived compounds that are known to have similar physiologically altering effects, including the byproducts of cleaning agents, cosmetics and plastics.

“We are showing that some of these chemicals can have much wider health effects on fish that we expected,” Tyler said in a statement.

Explaining how his team knows that these products have these unusual effects on the fish, Tyler added: “Using specially created transgenic fish that allow us to see responses to these chemicals in the bodies of fish in real time, for example, we have shown that oestrogens found in some plastics affect the valves in the heart.”

Antidepressants are also altering the behavior of fish in some rather unexpected ways. These drugs “reduce the natural shyness of some fish species, including the way they react to predators.”


Although not yet published in a peer-reviewed journal, the results of the research will be presented at the 50th Anniversary Symposium of the Fisheries Society, held in Exeter this week. It’s not hard to argue that this rather specific gathering is the ideal place in which to present this work for the first time.


  • tag
  • Rivers,

  • birth control,

  • intersex,

  • oestrogen,

  • contraceptive,

  • transgender fish,

  • toilets,

  • flush