Despite having known for almost two decades that pharmaceuticals are commonly found in aquatic environments (Kolpin et al. 2002), we are only beginning to understand the potential implications of these synthetic chemicals on aquatic organisms and ecosystem processes."

Source : Ecosphere, link below.

Traces of prescribed medicinal drugs (and their breakdown products - known as 'metabolites') are now widely found in aquatic environments.

They are excreted by the users and end up in sewage. In many cases, normal sewage processing techniques do not remove all traces before the water is re-cycled into waterways. The effects of these drugs on aquatic and marine organisms (and the wider food chain in general) are, for the most part, entirely unknown. As is the scale of the problem.

As an example, a 2021 study found that minute traces of the very widely prescribed anti-depressants known as Selective Serotonin Reuptake Inhibitors (SSRIs) (e.g. Fluoxetineplugin-autotooltip__plain plugin-autotooltip_bigFluoxetine

Fluoxetine is a Selective Serotonin Reuptake Inhibitor (SSRI) used in the treatment of Major Depressive Disorderand Obsessive-Compulsive disorder etc.. It's marketed under the trade names Prozac, Sarafem, Fontex and many others.

SSRIs are believed to act by inhibiting the re-uptake of the hormone serotonin ) could significantly be affecting the social behaviour of crayfish. See :Ecosphere Volume12, Issue 6.

A detailed, open-access report in the Proceedings of the National Academy of Sciences, 2022, which sampled rivers in 104 countries, found that the most common pharmaceutical residual chemicals were Carbamazepine (an anti-convulsant used to treat epilepsyplugin-autotooltip__plain plugin-autotooltip_bigEpilepsy

"Epilepsy is a chronic noncommunicable disease of the brain that affects around 50 million people worldwide. It is characterized by recurrent seizures, which are brief episodes of involuntary movement that may involve a part of the body (partial) or the entire body (generalized) and are sometimes accompanied by loss of consciousness and control of bowel or bladder function. Seizure episodes are a result of excessive electrical discharges in a group of brain cells. Different parts of … and neuropathic painplugin-autotooltip__plain plugin-autotooltip_bigNeuropathic pain

Neuropathic pain is caused by damage or disease in the nervous system. It's estimated that more than 5% of the global population is affected, often severely.

"Central neuropathic pain is found in spinal cord injury, multiple sclerosis, and some strokes. Peripheral neuropathies are commonly caused by diabetes, metabolic disorders, herpes zoster infection, HIV-related neuropathies, nutritional deficiencies, toxins, remote manifestations of malignancies, immune mediated disorder…) and Metformin (used to treat type 2 diabetes). Caffeine, which the authors term a 'lifestyle' chemical was the third most common.

Noting that :

[…] pharmaceutical pollution poses a global threat to environmental and human health, as well as to delivery of the United Nations Sustainable Development Goals."

See : PNAS 119 (8)