IT IS COMMON knowledge that smoking marijuana causes cravings for high-calorie snacks. The condition, known as the munchies, is a staple of popular culture. (Snoop Dogg, a rapper and notorious stoner, even penned a cookbook.) Yet empirical evidence of the phenomenon and its effects is scarce. Does getting high cause smokers to consume more junk food? And if so, by how much?

To answer this question, Michele Baggio of the University of Connecticut and Alberto Chong of Georgia State University examined state laws in America. Since the mid-1990s, more than 30 states have authorised marijuana for medical purposes and 11 have legalised it for recreational use. Because these laws were enacted at different times and in different places, they created a natural experiment for researchers to study the effects of marijuana—including its effect on food consumption.

With this in mind, Messrs Baggio and Chong collected monthly sales data from supermarkets, drug stores and other retailers in more than 2,000 counties across 48 states covering the period from 2006 to 2016. By comparing sales figures from neighbouring counties located along state borders—some where marijuana was legal and some where it was not—the authors were able to estimate the effect of marijuana legalisation on junk-food sales.

They found that after recreational marijuana was legalised in Colorado, Oregon and Washington, the only states for which 18 months of sales data were available, sales of ice cream rose by 3.1%, sales of cookies increased by 4.1% and sales of crisps jumped by 5.3% in the years after the laws were passed (see chart).