If you are only doing this once a week, I do not see the harm... But if you are doing this twice a day to stay awake, you might want to consult a doctor...

As a water soluable vitamin the chances of an overdose are less than that of a fat soluable vitamin.

But here are some signs you have had too much Niacin (B6):  Abnormal liver function; cramps; nausea; irritability.

All of the rest of the B vitamin complex has no known overconsumtion symtoms.