They aren't technically spots but areas of discoloration that would have spread to my teeth had I not stopped taking it. The dentist told me that long term use of various antibiotics can cause this type of thing. When he looked at my gums the first thing he asked was if I was on an antibiotic.

On a side note, my son went on it for his back acne or as we call it "bacne" and broke out in hives. He can't take it either.