Pantothenic Acid : Overdose...

Pantothenic acid is not known to be toxic in humans. No serious side effects have been reported, even at intakes of up to 10,000 mg (10 grams) per day.

Diarrhea

Very large amounts of pantothenic acid (several grams per day) can cause diarrhea. Doses of 10 grams (10,000 mg) or more a day can result in diarrhea.

No other adverse reactions to high doses have been reported.