Linus Pauling wrote many interesting books including Vitamin C and the Common Cold. He won a Nobel prize for chemistry in 1954 and another for peace in 1962 and was awarded many honorary degrees. His method to prevent the common cold is so successful, that I have not had one in about 7 years.
If symptoms disappear immediately, you may return to your usual regimen. If the symtoms return after you have stopped, start again immediately.
Ascorbic acid is inexpensive and harmless, and you may take up to 20 mg without harm. The only possible side effect is "loose bowels" if your body cannot use the amount taken. When this happens, just reduce your intake. It is a good habit to carry it with you and keep it at home, at work, in your car, and on your boat so you are never without it.