there's some literature to support taking "mega" doses of vitC reduces the severity/duration of "colds". by mega, i mean 1 gram or 1,000-2,000 mg.

In adults the duration of colds was reduced by 8% (3% to 12%) and in children by 14% (7% to 21%). In children, 1 to 2 g/day vitamin C shortened colds by 18%.

Authors' conclusions: The failure of vitamin C supplementation to reduce the incidence of colds in the general population indicates that routine vitamin C supplementation is not justified, yet vitamin C may be useful for people exposed to brief periods of severe physical exercise. Regular supplementation trials have shown that vitamin C reduces the duration of colds, but this was not replicated in the few therapeutic trials that have been carried out. Nevertheless, given the consistent effect of vitamin C on the duration and severity of colds in the regular supplementation studies, and the low cost and safety, it may be worthwhile for common cold patients to test on an individual basis whether therapeutic vitamin C is beneficial for them. Further therapeutic RCTs are warranted.

https://pubmed.ncbi.nlm.nih.gov/23440782/

for reference, Recommended Daily Allowance is 75 mg for women and 90 mg for men (probably average weight based).

i've mostly seen those packets and similarly dissolved in water/big doses recommended by nurses, but it was also brought up in my human nutrition class and endorsed. they are pretty cheap, they don't taste bad, and the body pisses out all the excess vitamin C so the chances of toxicty are negligible. i use them when i feel something coming on.