Trace Levels of Anxiety and Antidepressant Drugs Found in Drinking Water Worldwide

A glass of tap water may contain more than just H2O molecules and dissolved minerals. According to a new scoping review published in Environmental Science and Pollution Research, two of the world’s most widely prescribed psychotropic medications—the anti-anxiety drug diazepam and the antidepressant fluoxetine—have been detected in drinking water supplies across seven countries on three continents. The findings, compiled by a team of Brazilian researchers led by Paula Pinheiro Teixeira and Matheus Marcon at the Federal University of Triângulo Mineiro, suggest that pharmaceutical pollution has quietly penetrated the final barrier between environmental contamination and human consumption, and that the scientific community has barely begun to map the true scale of the problem.

The review, conducted according to the PRISMA-ScR guidelines for scoping reviews, searched seven major databases—CINAHL, Cochrane, Embase, LILACS, PubMed, Scopus, and Web of Science—without restrictions on language or publication year. The initial sweep identified 6,356 records, which the team whittled down through duplicate removal, title and abstract screening, and full-text eligibility assessment to just 13 original studies published between 2000 and 2024. Two additional studies were recovered by mining the reference lists of the included papers. The strict inclusion criteria demanded original field data on diazepam, fluoxetine, or haloperidol in actual drinking water samples, excluding laboratory experiments, bioassay-based detections, and studies reporting concentrations below the limit of quantification.

The headline numbers are striking in their scope rather than their magnitude. Diazepam was reported in eight of the 13 studies, with measured concentrations ranging from 0.2 to 24.91 nanograms per liter. Fluoxetine appeared in seven studies, spanning an even wider range of 0.2 to 300 nanograms per liter. The highest diazepam reading came from Chinese tap water, while fluoxetine reached its peak concentration of 300 nanograms per liter in both tap water and bottled water in a United States study. The earliest detection of diazepam dates back to 2000, when Italian researchers reported 23.5 nanograms per liter in the city of Lodi and 0.2 nanograms per liter in Varese. Fluoxetine made its drinking water debut in 2009, at 0.82 nanograms per liter in finished drinking water in the United States.

Geographically, the evidence is heavily skewed. China contributed five studies and the United States three, with single studies from Colombia, England, Hungary, Italy, and South Korea. The samples analyzed included tap water and finished drinking water in seven studies each, bottled water in two, and drinking well water in one. Notably, no studies at all were found on haloperidol, an antipsychotic included in the search strategy. The authors are careful to stress that this absence should not be read as evidence that haloperidol is absent from drinking water—it simply reflects a lack of monitoring data and research attention, a distinction that applies to much of the field.

How do molecules designed to alter human brain chemistry end up in the water supply? The review lays out a multi-pronged contamination pathway. A significant fraction of ingested psychotropic drugs is excreted unchanged or as pharmacologically active metabolites, primarily in urine, flowing into municipal wastewater systems. Wastewater treatment plants, which were never designed to strip out organic micropollutants, discharge these compounds into rivers, lakes, and reservoirs. From there, the drugs disperse through watersheds, infiltrate soil, reach aquifers, and can be drawn back into drinking water production systems—a recirculation loop that effectively closes the circle between prescription and tap.

Human behavior compounds the problem. Improper disposal of expired or unused medications—flushing them down toilets, pouring them into sinks, or tossing them in household trash—remains widespread despite take-back programs. The statistics cited in the review are sobering: roughly 39 percent of Canadian families reported improper disposal practices such as burying, flushing, or trashing medications; in Brazil, 76 percent of surveyed consumers discarded unused drugs in the regular trash, toilet, or sink; a Chinese survey of 6,293 households found that 44 percent had unwanted medications at home, and 89 percent of those families disposed of them in the trash, sink, or toilet; and in Saudi Arabia, 73 percent of respondents threw medications in the garbage. Pharmaceutical manufacturing adds another layer, with effluents from production facilities sometimes exceeding municipal wastewater concentrations by several orders of magnitude, creating localized contamination hotspots in regions with weak regulatory oversight.

The technical challenge of removal is central to the story. Conventional drinking water treatment plants are engineered primarily to eliminate pathogens, not synthetic organic molecules. Processes such as coagulation, flocculation, sedimentation, sand filtration, and chlorination are largely ineffective against psychotropic drugs, whose chemical stability allows them to pass through treatment trains intact. Studies of individual plants show highly variable removal efficiencies depending on the compound and the treatment configuration, and the review concludes that conventional processes alone are insufficient. Advanced technologies—ozonation, activated carbon adsorption, membrane filtration, and advanced oxidation processes—are typically required to achieve satisfactory removal, but these carry high capital and operating costs that limit adoption, particularly in developing countries where monitoring capacity is already thin.

Why should vanishingly small concentrations matter? The answer lies in the biology of the compounds themselves. Psychotropic drugs are deliberately engineered to be active at very low doses, and chronic exposure to environmentally relevant concentrations has been linked in laboratory studies to behavioral alterations in fish, disrupted growth and reproduction, oxidative stress, immune changes, embryonic and developmental toxicity, and bioaccumulation in aquatic species. Pharmaceuticals have been shown to accumulate in the tissues of aquatic organisms and biomagnify along food chains. Moreover, mixtures of drugs present simultaneously in water can produce synergistic or additive effects even when each compound individually sits at low concentration, amplifying potential ecotoxicological impacts in ways that single-compound risk assessments fail to capture. The potential human health consequences of lifelong, low-dose exposure through drinking water remain largely unexplored, a gap the authors flag as urgently requiring investigation.

The review also exposes a stark asymmetry in the global knowledge base. Psychotropic drug consumption is rising fastest in many developing regions—global sales of psychotropic medications grew at an average annual rate of 4.08 percent between 2008 and 2019, and the COVID-19 pandemic triggered a more than 25 percent increase in depression and anxiety cases worldwide, according to the World Health Organization, which now estimates that over one billion people live with a mental disorder. Yet the countries where consumption is climbing often lack the laboratory infrastructure, funding, and monitoring programs needed to detect these contaminants in their own water supplies. The result is a scientific record that maps pharmaceutical pollution mainly where researchers are already looking, leaving vast regions effectively invisible in the literature.

The authors frame their findings within the One Health paradigm, which integrates human, animal, and environmental health, and align them with the United Nations Sustainable Development Goals. Their prescriptions are concrete: expand water quality monitoring worldwide, improve analytical techniques capable of detecting ever-lower concentrations, invest in advanced treatment technologies, and implement public policies governing medication disposal and drug pollution. With forecasts pointing to substantial continued growth in pharmaceutical sales, the load of emerging contaminants entering water systems is set to increase. What the 13 studies assembled here reveal, the researchers suggest, is only the tip of the iceberg—a first, partial glimpse of a contamination problem whose full dimensions, impacts, and solutions the world has yet to measure, let alone manage.

Subject of Research: Occurrence of the psychotropic drugs diazepam and fluoxetine as emerging contaminants in global drinking water supplies

Article Title: Psychotropic drugs in drinking water? A scoping review of evidence on diazepam and fluoxetine

Article References: Teixeira, P. P., Pereira, B. A., da Silva Carneiro, R., de Assis, L. J. M., Leal, M. L., & Marcon, M. (2026). Psychotropic drugs in drinking water? A scoping review of evidence on diazepam and fluoxetine. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38296-5

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38296-5

Keywords: diazepam, fluoxetine, drinking water, emerging contaminants, pharmaceutical pollution, water treatment, psychotropic drugs, scoping review, One Health, wastewater, water quality monitoring, drug disposal