It’s one of marijuana’s most well-known side effects: the ravenous desire for food commonly called the munchies. But why does weed make chocolate, chips and, as the Harold and Kumar documentaries have shown, White Castle sliders so irresistible? Finally, science may have an answer.



The urge to eat is controlled by complex circuits of neurons in the brain. Some of these nerve cells make us feel hungry, driving us to eat. Others cause us to feel sated, so we put down the Doritos bag and stop filling our faces.



To figure out how marijuana might hijack this system, researchers exposed mice to a chemical that mimics the effect of the active ingredient in cannabis, THC, by binding to the brain’s THC receptors. These doped-up rodents tend to keep noshing, even if they’ve already eaten their fill. But what’s going on in their little mouse brains? Paradoxically, the researchers found that the cannabinoid receptor turns on the neurons that normally make animals feel full.



But what happens next is different from usual. When the “hey-I’m-full” neurons get triggered by the THC receptors, they wind up sending a “hey-I’m-still-hungry” signal that send us scrambling for the cupcakes. (This is your brain on drugs.)



In addition to explaining 4 a.m. diner trips, the research, in the journal Nature, may be useful for addressing the medical condition of appetite loss, as commonly happens with cancer and depression, for example. [Marco Koch et al, Hypothalamic POMC neurons promote cannabinoid-induced feeding]



Knowing these details of neuronal activity could lead to better treatments for those patients who could really benefit from a case of the munchies.



—Karen Hopkin



(The above text is a transcript of this podcast)



Scientific American is part of the Nature Publishing Group

