A friend gave me his Common Cold :( 

How do I know it's a Common Cold?  Because my doctor administered a nasal swab which eliminated other possible causes.  

Not to complain, but it has evolved into a hacking (barking) cough which was debilitating me until I started taking Musinex, which has alleviated the cough somewhat.  

The much overused "It is what it is" covers it, but why?  Why can't they cure the Common Cold?