Songwriters and novelists have long-claimed that love is a drug. Scientists have gone a step further to prove this. They conducted tests on the romantic relationships of prairie voles. Different pairs of the mouse-like animals were tested for levels of dopamine. This plays a role in our seeking pleasure and addictive things. The researchers said the voles released a lot of dopamine when they were with their "established partner". Dr Zoe Donaldson said parts of the voles' brains lit up "like a glow stick" when they were reunited with their mates.

The study helps to explain more about how complex human relationships are. It says dopamine plays a key part when falling in love, and in the sadness when breaking up with a partner. Dr Donaldson said: "Our entire social world is basically defined by different degrees of selective desire to interact with different people, whether it's your romantic partner or your close friends." She added: "Certain people leave a unique chemical imprint on our brain that drives us to maintain these bonds over time." Research also suggests that women get over breakups faster than men.