This abstract is for anyone considering doxycycline treatment for CFS or Lyme Disease or Protomyxzoa Rheumatica. Please be warned. http://www.ncbi.nlm.nih.gov/pubmed/18397263 It clearly states that doxy has a drastic effect on bifido bacteria populations in the gut. My doctor told me I had Protomyxzoa Rheumatica and put me on long term doxycycline. I had IBS pretty much my whole life and after six months of doxy it is the worst it's ever been and my acne (all over face, scalp, neck) is much worse. The bloating and gas, and abdominal pain and distention, and unceasing constipation are all the worst they've ever been. Especially at night when I look like I'm 6 months pregnant. I am so disappointed in my doctor who told me that doxy doesn't have much of an affect on the intestinal bacteria and told me not to worry about it. And then it turns out that I did NOT have Protomyxzoa after all. Why he lied to me, I don't know. I feel now like I'm more of a guinea pig than a patient. Everyone, please beware of doctors claiming they know what they are doing in treating Protomyxzoa with long term antibiotics. This has been a huge mistake for me.