I got one for a chronic cyst (a cyst would appear in the same place every month). The shot definitely made a difference and now the big cyst has been reduced to a small red dot for the past 2 months.
Sometimes a coritzone shot can leave an indentation that may be permanent, but it didn't for me.
I have not had a cortisone shot for a cyst, but I had a shot for a keloid scar under my chin. My derm had told me that it would take a series of 3 shots to make the scar go down, but to his surprise it only took one shot. I had no side effects and no indentation.
i go to my dermatologist for cortisone shots whenever i get a cystic pimple. works great! the pimple becomes flat the next day but it doesn't get rid of the red mark that pimples usually leave behind.