they merely often "symptom relief".
as you know, there's no cure for the common cold.
Around 800pc of your rda of vitamin c has been shown to shorten the length of the common cold by one day.
But I agree the benefit is mainly psychological.
..... and "one day" is all very well, but most colds are 4 - 8 days .
So you were bound to still have a cold today.
And, of course, there ends my "correct" little spiel. Consider yourself spoken to! :)