It takes between 2-3 hours to kick in. A bit less if you ate them with an empty stomach. But if you ate them with a full stomach, they may even dont work at all.

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"Everything we do, everything we are, rests on our personal power. If we have enough of it, one word uttered to us might be sufficient to change the course of our lives. But if we don't have enough personal power, the most magnificent piece of wisdom can be revealed to us and that revelation won't make a damn bit of difference." Don Juan Matus - Tales of Power