The effects of antidepressants on wildlife are currently raising some concern due to an increased number of publications indicating biological effects at environmentally relevant concentrations (<100ng/L). These results have been met with some scepticism due to the higher concentrations required to detect effects in some species and the perceived slowness to therapeutic effects recorded in humans and other vertebrates. Since their mode of action is thought to be by modulation of the neurotransmitters serotonin, dopamine, and norepinephrine, aquatic invertebrates that possess transporters and receptors sensitive to activation by these pharmaceuticals are potentially affected by them. We highlight studies on the effects of antidepressants, on particularly crustacean and molluscan groups showing they are susceptible to a wide variety of neuroendocrine disruption at environmentally relevant concentrations (pg-ng/L). Interestingly some effects observed in these species can be observed within minutes to hours of exposure. For example, exposure of amphipod crustaceans to several selective serotonin reuptake inhibitors (SSRIs) can invoke changes in swimming behaviour within hours. In molluscs, exposure to SSRIs can induce spawning in male and female mussels and foot detachment in snails within minutes of exposure. In the light of new studies indicating effects on the human brain with just of dose of SSRIs using magnetic resonance imaging (MRI) scans, we discuss possible reasons for the discrepancy in former results in relation to the “read-across” hypothesis, variation in biomarkers used, modes of uptake, phylogenetic distance, and the affinity to different targets and differential sensitivity to receptors.