Dude, am I stoned? An app that tests memory, attention and reaction – traits that are often impaired by cannabis use – aims to answer that question by giving people a measurement of how well (or badly) they performed.

Cannabis is now legal in a small but growing number of countries. Researchers at the University of Chicago made the app in the hope that it will make cannabis use safer , helping those who take it understand how the drug is affecting them. “One of our long-term goals is …