If you want to make your own remedy, here are two variations on the same theme. In both cases, people who use it swear by it and say it keeps indefinitely. These are recommended when you feel like you might be coming down with something. Be very careful about your fingers so they don’t end up with cayenne on them!
(1) Combine 2 tsp cayenne pepper, 1 ½ teaspoons salt, 1 cup water, and 1 cup apple cider vinegar in a saucepan and heat the mixture over direct heat just until the salt dissolves.
Keep it in a jar in the refrigerator preferably.
This stuff is VERY HOT – as in spicy — so try a little bit at first; you can dilute it with water. At the first sign of a cold or flu, take between a teaspoon to a tablespoon every half hour for a while, then every couple of hours. If giving it to children, smaller doses are appropriate.
(2) Grate a ginger root and add several tablespoons of hot cayenne pepper powder. Put these in a quart jar and fill with vodka. For your first batch, you might do about half as much.
Cover the jar tightly, keep it in the dark, and shake it every day or two for several weeks. At that time, put some of it in a dropper bottle and take a squirt or two (or mix it in water for a less fiery experience) when you feel something coming on. This is said to also help with digestive upsets.
Your mileage may vary, this isn’t medical advice, etc etc.