Pharmaceuticals in the environment

Active Pharmaceutical Ingredients (APIs) are metabolised in the human body. Metabolism refers to the chemistry occurring in our bodies, and that of all organisms. Metabolism converts food into energy and substances such as muscle and fat. Metabolism is also responsible for removing wastes from the body. APIs are also subject to metabolism because enzymes will convert unfamiliar or excess substances into easily excreted chemicals. Typically, the API will be converted into a more water soluble substance so that the body will expel it in the urine. 

The degree of metabolisation varies greatly between APIs and between the method of administration (e.g., topical products are hardly metabolised). After use, APIs and their metabolites are excreted by patients or topical treatments are washed off (by showering or the washing of clothes). These substances then enter the sewage system. Sewage treatment plants can only partially remove these pollutants, leading to emissions into the aquatic environment. Routes of APIs into the environment are summarised in this infographic from the book 'Medicines and the environment: challenges and solutions for sustainable pharmacy' (Hanski et al., 2025).

The presence of pharmaceuticals in the environment has been discovered worldwide, with high concentrations in regions with limited sanitation, and lower concentrations in regions with improved sewage treatment facilities. 

As APIs (and, mostly to a lesser degree, also their metabolites) are specifically acting as bioactive chemicals, they may also have these effects on environmental organisms. This could be the same effect of the medicine intended in human patients, but also secondary side effects are known. Because of the continuous presence of pharmaceuticals in low concentrations, effects on aquatic organisms are usually not lethal but involve more subtle effects like reproduction, growth, and behavioural changes. 

Risks presented by APIs in the environment depend on both occurrence (exposure) and effects of a substance in a given environmental setting. For highly active compounds like hormones and psycho-active drugs, risks could be expected to occur even at extremely low concentration levels. However, the risk to the environment for less potent drugs may be widespread when the use (and resulting exposure concentrations) is high enough. For example, the presence of anti-inflammatory API diclofenac exceeds the proposed environmental quality standards at half of all monitoring locations in the Netherlands (Faber et al., 2024). The feminisation of fish is one well documented issue of pharmaceuticals in the environment (see video below).