I always found I did better on tests while I was still intoxicated from the previous night.
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It worked for me
See, this guy gets it!
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It's all about the person. I know several people who can't do more than eat Jethro Bodine sized bowls of cereal when they are stoned. The group of people I ran with, when we got high, we were inspired. We'd often help each other with task ranging from cleaning their room, doing homework, or even working on their car. Weed made us active, but I do think of us as a rarity when speaking on the topic.
It's all about how your body reacts to the substance. If you know it'll be a mess, then you should not do it. For me, I was fully functioning in school when I was high or sober.