Writers of novels and songs have for centuries claimed that love is a drug. Scientists have now gone a step further to prove this assertion. They conducted tests on the romantic relationships among prairie voles. Different pairs of the mouse-like rodents were tested for levels of dopamine – a neuro-transmitter that plays a role in our seeking pleasure and a craving for addictive things. It can provide an intense feeling of reward. The researchers found that the voles released large amounts of dopamine when they were physically with their "established partner". Researcher Dr Zoe Donaldson said parts of the voles' brains lit up "like a glow stick" when they were reunited with their mates, and dimmed when with unknown voles.

The researchers said their studies help to explain much about the complexities of human relationships. They say dopamine in our brains plays a key part when falling in love, and in the grief experienced when breaking up with a partner. Dr Donaldson said: "As humans, 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: "This research suggests that 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 a breakup, and fall out of love faster than men.