You know when after a run you feel great? Well previously scientists thought this runners' high was down to endorphins, but this may not be the case. Johannes Fuss from the University of Heidelberg found that mice that ran around all day felt less pain and less anxiety - key features of a runner's high. However, this feel good sensation wasn't down to endorphins, but endocannabinoids - the same chemicals that come from smoking cannabis! Rosalind Davies jogged on over to find out more... Like this podcast? Please help us by supporting the Naked Scientists