(Newser) – Hanging out in marijuana cafes and smoking the night away is not exactly good for your grades, especially in math, according to a new study. Researchers drew this conclusion after comparing more than 54,000 grades of undergraduates in the Dutch city of Maastricht, where some were banned from the city's 13 cannabis coffee shops, the Guardian reports. The upshot: The banned students had a 5% better chance of passing courses. For weaker students, the improvement in their chances rose to 7.6%. And the overall effect was a stunning five times higher for courses involving numbers and math. "The effects we find are large, consistent, and statistically very significant," says study co-author Olivier Marie. "The grade improvement this represents is about the same as having a qualified teacher."

Marie says it's hardly surprising, since we already know that THC (the main psychoactive ingredient in cannabis) affects cognitive functioning. But this comes at a key moment, as more than 20 states in the US permit weed for medical use, four states allow recreational use, and Uruguay may become the first country to totally legalize cannabis. The finding could also inform the debate over THC levels, which are getting higher. "I think it is reasonable to at least inform young users much more on consequences of consuming such products," says Marie. An amusing side note: The study says that students from France and Luxembourg had been banned from the cafes for being "drug tourists" and "creating the most nuisance" for locals, the Independent reports. (Read about a drug that could "top" medical marijuana.)

