Writers have long-claimed that love is a drug. Scientists have gone a step further to prove this. They did tests on the relationships of prairie voles. Different pairs of voles were tested for levels of dopamine, which plays a role in our seeking pleasure. The researchers said the voles released a lot of dopamine when they were with their "established partner". Parts of the voles' brains lit up "like a glow stick" when they saw their mates.

The study shows how complex human relationships are. It says dopamine is released when we fall in love. A researcher said: "Our entire social world is…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." Research also suggests that women get over breakups faster than men.