depression
"I have suffered from major treatment-resistant depression for 32 years.  I've tried so many medications along with polypharmacy for this, and almost nothing helps.  The only antidepressants that are of any use are citalopram, buproprion, and Abilify.  Even this combination doesn't always work--usually the citalopram stops working after a number of months, and I have to switch it out for sertraline.

A few years ago, my psychiatrist tried adding 20 mg of methylphenidate twice a day.  What a difference!  I am now able to get out of bed, work, focus, smile, and have something that approximates a normal life.

The only problem with this, is that I am now completely dependent on the methylphenidate in order to function."