During normal patient use of medicines, non-metabolised substances are excreted and emitted into the sewerage system following use. The compounds may then be released into surface waters or enter terrestrial ecosystems when sewage effluent is emitted to river systems or used for irrigation or where sewage sludge is applied as a fertilizer to agricultural land. Consequently, a variety of APIs have been detected in the natural environment across the world. Although reported concentrations are generally at trace levels, many APIs have been detected in a variety of hydrological, climatic, and land-use settings and some have the potential to persist in the environment for months to years. APIs are biologically active compounds that are designed to interact with specific pathways and processes in target humans and animals. Concerns have therefore been raised about the potential effects of APIs in the environment on human and environmental health. Over the past 15 years, a substantial amount of work has been done to determine the occurrence, fate, effects, and resulting risks of APIs in the environment. Regulations have also been developed regarding the assessment of environmental risks of APIs and the pharmaceutical industry has conducted testing to meet these regulatory requirements.