Contaminants are known to alter a range of fitness-related traits, including behaviour, in wildlife. An emerging and potentially potent class of contaminants is pharmaceuticals. Following consumption, a proportion of many pharmaceuticals are excreted unmetabolised. Sewage treatment works and fields fertilised with sewage sludge attract many foraging birds because of the abundance of invertebrate prey. Some pharmaceuticals, including the commonly prescribed antidepressant Fluoxetine (FLU), are persistent in the environment and can accumulate in invertebrates. FLU is designed to alter human behaviour at low concentrations and causes a range of side effects. To assess the impacts of FLU-contaminated prey on wild birds, we fed wild-caught starlings Sturnus vulgaris an environmentally relevant concentration of fluoxetine over 16 weeks. Assayed over two days in isolation, exploration in a novel environment, responses to human disturbance and activity levels were unaffected. Fluoxetine did affect the physiological responses of FLU-treated birds in terms of their habituation to isolation stress compared with controls. In their home aviaries, controls increased their foraging rates at times of peak nutritional stress, as seen in other avian species during winter. The FLU-group, in contrast, did not vary their feeding rate over the day, thus their foraging behaviour showed them to be less sensitive to the risks of starvation and predation. Finally, we found evidence that FLU altered courtship and social behaviours compared those of controls. Our data suggest that exposure to fluoxetine disrupts the relationships between corticosterone, feeding behaviour and body mass regulation in birds, thus altering risk sensitivity. Fluoxetine is one of many psychoactive drugs found in sewage which have the potential to alter the behaviour of wildlife. However, behavioural endpoints are currently not accepted in risk assessment of pharmaceuticals. A key next step is to demonstrate that contaminant-induced alterations to behaviour both impact upon individual fitness and population dynamics.