You need two humans for romantic love. That sounds straightforward enough. But you also need chemistry, as in chemical processes. It is an uncomfortable thought in a society where freewill is all the rage. Yet any of our feelings need a basis on which to work upon. And that is our brain with all its neuronal circuits and neurotransmitters that are being continuously fired from one neuron to another, sending messages of fright, anguish, enthusiasm, sadness, despair, love and surprise to name but a few. So what would be the chemistry at the heart of romantic love? Serotonin. Perhaps… With a notion as ungraspable as love, it is a very tricky business to try and pin it down to the makings of one molecule. Yet that is what a team of scientists tried to do. Their research hypothesis is particularly intriguing: they compared the infatuation we all experience in the early stages of love with a form of obsessive-compulsive behaviour.