Spironolactone
"When I was a teenager I had *mild* cystic acne---mild meaning I would only get one or two cysts a month, but the ones I did get were huge, red, painful, ugly, and often left a scar.  Years later, approaching the age of 30 and having exhausted every treatment under the sun, it was not getting any better.  My dermatologist suggested Spironolactone (100mg/day)... My skin got worse for the first few weeks, almost like my body was expelling everything... but I stuck with it and it's been a MIRACLE!!  My skin is smooth and acne-free.  The only side effect is I'm groggy for a few hours so I take it at night.   Don't give up on it if things get worse initially, it is a hormonal treatment and might take a while for your body to adjust.  I LOVE it!!"