Doxycycline
"I've been on doxycycline (100 mg daily for three months) twice, a year apart. The first time cleared my skin up beautifully. I had horrible cystic acne with new pimples popping up every day before I went to my dermatologist. I started clearing up within the first month. A year later, I started to break out again so I went back on it and my skin is back to being clear. I definitely recommend taking it with food, though. I got really bad heartburn for a week because I took this pill without eating."