I experimented 5+ years with it and took on several occasions 100+g per day with regular input between 10-15g per day.
The only problem I had after 5 years is slight pain in esophagus immediately after taking C, but it passed after I switched to taking C on full stomach.
Note: you MUST use pure AA powder, nothing else. Timing of C is essential - you must do it right, or the effects are minimal (you basically have to simulate the liver ancestral production now disabled in humans).
Vitamin C is a miracle thing IMO, especially 4 kids. My daughter was taking 1g since age 1 (now has 5) and she has remarkable health (she is sick once or twice per year for 2-4 days without any complications with being in kindergarten with 30+ kids since age 1, although the non-vitamin-c factors are contributing to this picture quite a bit).
Vitamin C is the most effective virus killer in large doses if you time it right. It is poor antibiotic but you have many options in plant world for that.