Limpets are being killed due to the rise in antidepressant use which means they struggle to cling onto rocks, scientists have warned.
A new study argues that aquatic creatures in and around the UK are now "bathing in a soup" of the drugs after prescription rates doubled in the last ten years.
Experts have called for doctors to consider the effect on the environment before offering medication such as Prozac, saying its presence in the ecosystem can affect everything from a creatures' growth and shape to its movement and feeding habits.
They also point to research indicating that antidepressants in waste water have caused shrimps to swim towards light, making them more likely to be eaten by predators.
Similarly, the chemicals have been linked to aquatic species no longer being able to stick to surfaces such as rocks.
It is thought that approximately six million people - around 10 per cent of the population - now take antidepressants regularly.
Published in the British Journal of Psychiatry, the new study calls for an overhaul of the UK's waste water system to bring chemical levels to within legal levels, as well as encouraging patients to return unused medication to pharmacies rather than flushing down the lavatory.
Professor Alex Ford, of Portsmouth University's Institute of Marine Biology, said: "Antidepressant and anti-anxiety medications are found everywhere, in sewage, surface water, ground water, drinking water, soil, and accumulating in wildlife tissues.
"They are found in sea water and rivers and their potential ability to disrupt the normal biological systems of aquatic organisms is extensive.
"This isn't about a one-off pollutant entering their habitat; wildlife are bathed in drugs for their entire lifecycle.
He added: "Laboratory studies are reporting changes such as how some creatures reproduce, grow, the rate at which it matures, metabolism, immunity, feeding habits, the way it moves, its colour and its behaviour."
Scientists believe that aquatic organisms can be affected by as little as one nanogramme of the drugs per litre, the equivalent of a few drops of water in an Olympic-size swimming pool.
It is thought that, just as antidepressants affect hormones such as serotonin in the human brain, they affect serotonin in invertebrate creatures.
Research has also indicated that the drugs affect the species' ability to reproduce.
"Toxicity levels of pharmaceuticals in the environment do not necessarily relate to high concentrations, but to their constant low-level discharge, persistence in ecosystems and highly active biological functions," said Professor Ford in a linked editorial.
"In this way, pharmaceuticals that are found in relatively low concentrations could be extremely potent and very persistent, and able to significantly affect non-target organisms."
The researchers suggest that the increase in antidepressant use is partly due to the difficulty in securing psychological counselling in the UK.
They argue that prescribing the drugs should be reduced in favour of counselling as far as is safe for patients.
The majority of antidepressants enters the environment having been excreted into the sewage system, with even the most modern plants unable to adequately extract traces from the water.