Sulfamethoxazole / trimethoprim
"It's the silver bullet! Well, for me at least. I can only add my highest recommendation for Bactrim to treat my cystic acne, the kind that produces cysts around 2-3 cm in diameter all over my body and face. I've been on Accutane and every other antibiotic there is, but the Bactrim has saved me. It is hard on your digestive system, and I still haven't come up with a good solution for that yet, but I can certainly live with it if it means no more painful cysts which need to be cut out and operated on medically (no fun at all). 

I've always had cystic acne, but the Bactrim seems to kill the bacteria that produce the cysts, so as long as it keeps working I'm happy."