25 mg of Benedryl or even just half of a 25-mg tablet of
Benedryl...unless you are REALLY sensitive to it and it'd keep you sleepy into the time of your exam. If you think you might be really sensitive to it, I'd try just a third or a fourth of a 25-mg tablet.

The same is true for the Tylenol PM BCG mentioned; if you're afraid you'll be too sleepy if you take something this late, you could try even just half of a Tylenol PM.

BTW, good luck on your exam!

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