And actually, in terms of intractable coughs, morphine is not "snake oil". Any opiate does an excellent job of suppressing coughs. Of course, often you actually want the cough to do its job, but I've had one or two bouts where the cough was the problem, rather than the underlying lurgie.
Unidentified substances in your cough syrup aren't the way to go, however. I just pop a couple of Panadeine unless you can get a doctor to prescribe the good stuff (syrup with codeine).