Who could have guessed such a thing would be true?

The Connecticut Post reports:

Yale study: High students, low grades

News flash: College students who spend a lot of time drinking and smoking marijuana might not have the best grades. This not-very-shocking finding is at the heart of a new study conducted by researchers from Yale University and Hartford’s Institute for Living.

But those behind the project said the topic is a bit more complicated than it might seem.

The study, which was largely funded by the National Institutes of Health, followed 1,100 college freshman in Connecticut over four semesters, and asked them questions online about how much alcohol and marijuana they used each month.

“One reason we wanted to focus on this area of study is that it’s very unique, in that not a lot of researchers have data on alcohol and marijuana use,” said Shashwath Meda from the Institute of Living, the study’s first author.

The students ended up falling into three clusters — those who drank little or no alcohol and smoked little or no pot, those who drank moderately or heavily but used marijuana infrequently, and those who used both substances moderately or heavily. There was little effect on grades in the first two clusters, but the grades of those who drank and smoked pot suffered the most.