A study in mice has provided the most complete explanation yet for why a spliff triggers intense hunger pangs. The findings, which elucidate the role of smell, also suggest that we might eventually be able to treat common disorders such as obesity and loss of appetite with a simple nasal spray.

We know that the active ingredient in cannabis, THC, binds to cannabinoid receptors in the brain called CB1s. This binding inhibits chemical signals that tell us not to eat, and so make us feel hungry.

But this isn't the end of the story. Since smell plays such a central role in making us feel hungry, it must be part of the explanation - but no one knew exactly how it fit.