Like Col. Derontchi said, don't just memorize it. Look for meaning. Make connections.
Try to study in an environment which is similar to the environment where you'll be tested. Or, when being tested, think about the room where you studied the material. You make associations with the place you learned.
Are you getting sleep and drinking water? If you're lacking either of those, it could have a huge impact on how effectively you study.
I get the sense that people who smoke weed every day are fairly relaxed. I know that this is much easier said than done, but try to relieve some of the anxiety. If you're constantly worrying about failing, you're not thinking about the material.