Jamie, I've taken a high dose (2 to 4 g.) irregularly for over 20 years to cure/prevent colds & it also works for hay fever.
If I take too much it is a similar effect to eating too much fruit .
A study in USA of very high dosage users over many years found that the only other side effect was that crystalls formed in the kidneys of some users which disappeared when the Vit. C was stopped.
Regards,
Max.