What Causes Black Dots All Over The Body?

My 92 yr. old Mother developed black spots over her body. Went to her Dr, yesterday. Did blood work and took
her off a medication. This morning the spots are gone ! I live out of state from her and she can't think of what the
med. was for. Would you have any idea what was the cause and how quickly the spots disappeared ?
Thank you for your help, Concerned daughter in Atlanta.