For colds or impending colds:
My recommendation is good old fashioned home-made chicken soup.
In a pot place a whole chicken, pour enough already boiling water to cover and a bit more, turn on fire and bring just to boil, and then turn down the fire to let the soup cook just at the point of boiling
Just after turning on the fire, throw the following vegetables into the soup:
sliced celery (2 or 3 stalks)
sliced carrot (2 or 3 stalks)
sliced onion (2 or 3 whole onions)
crushed garlic (one head per chicken)
dill (1 tablespoon)
parsley (2 tablespoons)
After the soup has cooked for an hour, add salt and pepper to taste.
Cook the soup for two hours.
Let cool enough that fat solidifies, and then skim off fat. Keep soup cold or freeze in bowl-sized dosages. Serve piping hot and watch the cold go away in REAL TIME!
PS: Since 1990, when I stopped taking pills as a cold rememdy, any time I have been able to take this kind of chicken soup during the first few hours after feeling the first scratchiness of a cold, the cold has gone away with the eating of the chicken soup. In these cases, I had a cold for only about 4 hours while the soup was being made. In that same period, any time I have not been able to get the chicken soup into me during those first few hours, I have been stuck with the cold for around 5 days. However, this 5 day sickness is shorter than the 7 to 14 days I was spending with a cold when I took pills.