bacterial infection
"Doxyclycline has been the only antibiotic that has helped me consistently clear my severe sinusitis with excessive catarrh and phlegm (even when I was told it was viral) - over 15 years.  Once every couple of years or so I have had infections that simply don't clear without help.  I have been prescribed many other antibiotics and all that happens is I have to finish the unhelpful course (with no result) and then use Doxycycline.  Over years, I have endured the ridicule of several doctors who explain how this cannot help me - I then have to find a doctor who listens - then I can breathe again."