Figured I'd throw forth this little family recipe I just coaxed out of my grandmother. She says this is what her grandmother, who was the midwife and herbal-remedy person around La Cienega, NM, would make when anyone had a cold.
Lemon
Honey
Boil together into a tea. For very serious colds and flus, replace the honey with onions. (She is said to have saved a lot of people in the 1918 Flu Epidemic with her onion mixture.)