A hormone found in chocolate could be the 'mental Viagra' that helps to get couples in the mood for sex.

在巧克力中发现一种堪称“精神伟哥”的激素，可以让爱侣们性欲大增。

Kisspeptin, which is found in chocolate, is the hormone in the brain which kickstarts puberty.

And it may explain something about the behaviour of teenage boys, after scientists found it makes men much more interested in sex and relationships.

Young men injected with the hormone and then given brain scans showed a flurry of activity in the parts of the brain activated by sexual arousal and romance.

It means similar injections could be used to help men to start a family.

Professor Waljit Dhillo, the lead author of the research from Imperial College London, said: 'Our initial findings are novel and exciting as they indicate that kisspeptin plays a role in stimulating some of the emotions and responses that lead to sex and reproduction.

'Ultimately, we are keen to look into whether kisspeptin could be an effective treatment for psychosexual disorders, and potentially help countless couples who struggle to conceive.'