Doxycycline
"I started taking this drug when my acne got worse. Before that, I had only tried topical acne treatments (b.p, erythromycin) which worked well at first but later became ineffective. I had several cysts and pustules by the time I started this drug, it healed my cysts fairly fast but broke me out in pustules. After the two month mark (I took it for 3), my acne had decreased noticeably. I was really happy for about a month after I was done , until my acne came back much much worse. 
I'm not saying this drug is definitely the reason, but logically speaking, my acne was never this bad. It was very cystic, inflamed and painful. I was crying every day and not going out. Then my dermatologist started me on isotretin, which I'm still currently takin"