underactive thyroid
"I've been on this medicine for almost, but not quite, 10 years.  It is night and day comparing how I am now to how I was before I was diagnosed and treated for hypothyroidism.  My hair loss has stopped, my skin and nails aren't as dry and brittle, I can think clearly most of the time and I have energy again.  It took a while to get to the right dose, I've been both too low and too high.  But I'm stable and feeling pretty decently now."