Acne
"I took Doxycycline for severe cystic acne for six months.  My skin cleared up beautifully, however once I stopped taking it, within a week, my skin broke out 10x worse than it was before I started taking Doxycycline.  I ended up not only with the usual painful cystic acne, but also on top of that developed acne rosacea... So my face was lumpy, painful, and terribly red."