A persistent cough after a cold or the flu can be a frustrating experience. Coughing that comes with an upper respiratory infection goes away eventually, but those two, three, four, or even six weeks of suffering can be miserable.
If you are 30 or older and it seems like it takes longer get over the coughing induced by a cold than it used to, it probably does. From about 1885 until the early 1990's, most North American cough syrups contained either codeine or an expectorant called terpin hydrate.
An expectorant is just something that loosens up phlegm in the lungs and makes it easier to expectorate, or cough up. Terpin hydrate, as it name suggests, was derived from oil of turpentine and the essential oils of eucalyptus, oregano, and thyme.
In the 1990's, unfortunately, the US FDA decreed that one hundred years of mothers giving terpin hydrate to their children counted for nothing, that there was no evidence that terpin hydrate worked. You can't find this venerable old ingredient in cough syrups in the US today. (What you can find is dextromethorphan, which the US FDA approves despite the fact there's no evidence for its working, either.)
Where you can find a very similar remedy, however, is Vicks VapoRub. It contains eucalpytol, thymol, and oil of turpentine, like terpen hydrate did, and also contains camphor, cedarleaf oil, menthol, and nutmeg oil. You don't take Vicks by mouth, however. You rub it on the chest or own the soles of the feet.
Exactly why Vicks should work when it's rubbed on the soles of the feet is something of a pharmacological mystery, but it does. Just be sure to put socks on feet to protect bedsheets and mattresses.
Some other home remedies?
•There's always chicken soup. I have an entire posting on why chicken soup cures colds.
•Some people find that dark chocolate eaten in nibbles, or purple grape juice drunk in sips, relieves coughing. Scientists speculate that the sweet taste actives that brain's endorphins to calm a cough. Chocolate and grape juice are certainly a pleasant way to get over a cold--just beware of allergies.
•Another old-fashioned favorite is horehound candy (also known as marrubio, if you're buying it in a Mexican hierberría). The bitterness in the candy is just enough to activate a reflex that both releases stomach acid and reduces the secretion of phlegm.
•Ginger tea is at least as effective against cough as any cough medication containing dextromethorphan.
Codeine cough medicine is still available, but only with a prescription. It's inexpensive, from US $5 to $10 a bottle, but it has some drawbacks. Codeine can cause constipation, upset stomach, and drowsiness, and it's habit-forming.