If youre pregnant and take 8 tylonal at once, will that cause birth defects or miscarriage?

No: It will not cause birth defects or miscarriage, but it could cause liver failure! 8 tylenol is too many to take at one time. You should never take more than 1000mg at one time, and should avoid taking more than 3000mg per day, as it can damage your liver. Regular tylenol is 325mg per tab, so 8 of those would be 2600mg - way too much to take at one time!