Clinically, it is well recognised that neuropsychiatric disorders – and the drugs we use to treat them – frequently affect appetite. While our precise understanding of how specific disorders affect appetite and weight regulation is still at an early stage, we now have a framework that can in part explain the findings from genetic, experimental and clinical studies. The ultimate goal of eating is to obtain and then store enough energy to survive and reproduce as a species – as such, the neural circuits that defend against starvation are hard-wired in our brains. Adipose tissue-derived hormones, which provide information about nutritional state and hormonal and neural signals generated by meal consumption, act in combination on neuronal circuits in the hypothalamus and brainstem which express specific receptors and ion channels on their cell surface (). The function of these neurons can also be regulated by a range of neurotransmitters (e.g. serotonin, dopamine, histamine, noradrenaline), which are released by neurons that project widely throughout the brain. In this way the neural circuits which regulate appetite are intricately connected to the circuits that regulate mood, anxiety and behaviour.