False. This was discussed in my college psychology class and the effects on the mind. If people who smoke marijuana seem like idiots it's because they're inconsistent, like so: Someone is in class high during a lesson, but shows up for the test sober they'll do worse. If they show up high for the test as they did for the lecture, they'll do better. The same applies for sobriety and taking the tests and lecture. That, and if someone stops smoking marijuana after years of smoking, they still maintain the same learning abilities as someone who's never smoked. They simply might have some catching up to do if they weren't consistent about it.