Pharmaceuticals are a large group of chemicals used either by humans for personal health or by agribusiness to enhance the growth and health of livestock. Pharmaceuticals are considered to be emerging environmental contaminants. Indeed, several studies have shown that these compounds continuously enter aquatic ecosystems. Both pharmaceutical consumption and erroneous discharge of unused or expired medications make notable contributions to the introduction of pharmaceuticals into the environment. Additionally, pharmaceuticals consumed by humans and livestock are not entirely absorbed by organisms and are excreted and passed into wastewater and surface water. Although most pharmaceuticals are designed for human consumption, they can affect non-target organisms that share certain homologous receptors with humans. This review intends to summarise the most recent information concerning the effects of some classes of pharmaceuticals on the immune parameters of aquatic invertebrates.