How dangerous would it be to overdose on caffeine pills?

by one pill. I get tired a lot and energy drinks arent working and neither is coffee that mcuh. When the caffeiene pills stop working how dangerous would it be to just take one pill extra? Sources?
Update: Is 5-10 grams close to 200 miligrams (mg)?
Update 2: what about 450mg of caffeine? Is that safe to take?
Update 3: The doctor says I'm tired because I'm on chemotherapy. She won't prescribe me with anything to boost my energy though.
Update 4: I also need these to speed up my metabolism to lose weight faster.
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