So, are the old ways always the best? Well, sometimes they make sense even if you can't prove it. Then again, sometimes they don't.
Discover Magazine has an article on medical remedies in the old days, based on the book How to Cure the Plague. The author, Julian Walker, explores the science behind a wide range of history's cures. A couple are below - more at Discover.
Herbal Cough Syrup:
Take a pot of barley, and seethe it in a gallon of well-water, and let it seethe until the barley be lost; then strain it and put thereto as much new wort as of the aforesaid licquor, and put therein a good quantity of sage, and as much hyssop, and a pennyworth of liquorice well bruised; then seethe it again until it be half consumed away; then strain it and put it into a glass, or into some other close vessel, and so let it stand the space of one whole day, and let the party grieved drink two or three spoonfuls of it at a time, both morning and evening, and this will help him in a short space. This hath been well proved.
– A Rich Storehouse, or Treasurie for the Diseased, 1607
'Wort' is unfermented beer – the mix of grain and water, which would be soothing to drink; hyssop is a good expectorant, while sage has long been used against fevers. Liquorice’s soothing properties mean that it is still a common ingredient in cough medicines.