== As a Pollutant ==
Because humans and animals often do not fully metabolize pharmaceuticals in their body, they can excrete drugs or their breakdown products, which may the enter the environment.<ref>O.A.H. Jones, N. Voulvoulis, and J.N. Lester, [http://www.geol.lsu.edu/blanford/NATORBF/14%20Pharmaceuticals%20and%20RBF/Jones%20et%20al_Crit%20Reviews%20Env._2005.pdf Human Pharmaceuticals in Wastewater Treatment Processes], ''Environmental Science and Technology'', 2005.</ref>
=== In Sewage Sludge ===
=== Breakdown in the Environment ===