Benzoyl peroxide / clindamycin
"As far as the medicine doing what it is supposed to do, it's great.  It dries acne (even severe acne, in my case).  Unfortunately, it also caused me to have systemic side effects - rare, but they do happen.  I developed ringing in my ears and had to stop using it.  After a month I tried using it again, and the ringing returned.  I've been keeping careful track of my usage of it and the episodes of ringing in my ear, and they match.  I'm probably one in a thousand that this has happened to, but being a musician, I need to be able to hear.  My dermatologist and I will be meeting next week to discuss this and see if there are any other options for me."