This talk will examine the effects of two commonly found pharmaceuticals in waterways - the antidepressant fluoxetine (Prozac®) and the antihistame diphenhydramine - on the growth and photosynthesis of the common green alga, Scenedesmus. At environmentally relevant concentrations i.e. commonly found worldwide in urban streams, these drugs can have major effects on phytoplankton (and biofilms). In laboratory growth experiments, the effects of one drug in particular are quite startling. The mechanism for this will be discussed along with implications for food webs and future research in this nascent field.