There’s a sort of urban myth among students that cannabis can somehow help you to learn and pass exams. Everyone knows someone who knows a person whose cousin’s friend got 12 A*s and 3 distinctions because they sat their exams while off their head on some kind of drug- usually cannabis. Well according to new research, students that use cannabis tend to fail their university courses more often than students that don’t.

The experiment was conducted at Maastricht University in a part the Netherlands that borders Belgium, France and Germany. Many cafes in the Netherlands are licensed to sell weed but Dutch law means that only students that live in the Netherlands can buy cannabis whereas Maastricht University students that live over the border can’t. This law only recently came into place so researchers were able to monitor the change in grades of German, French and Belgian students that used cannabis before the new rules and Dutch students who could still use cannabis. Students that used cannabis performed up to two grades worse but the study found that students that no longer used cannabis were 5% more likely to pass their courses and the biggest improvements came from females and underperforming students.

Whether the poor academic performances from cannabis users comes from the actual drug and its effects or other factors is unknown. What seems to be for sure is that if you want the best grades, keep the weed out of your brownies.