Did you give them a written resignation letter you still have on file? Do you have something, in writing, saying that this employer claimed you were fired for drug use or at least contact information for a person telling you this is what they said?
You might have a claim for slander and tortous interference with a business contract if this has arguably costs you other employment provisions. However, given the expense of litigation and time involved, you may just want to consult with an Ohio attorney to see if they can 1) ask that your former employer provide documentation supporting their claim that you were fired for drug use as opposed to resigning 2) otherwise cease and desist from given such false information in the future and give a neutral job reference that merely confirms your prior employment and the period of time of your employment.
You need to nail down your evidence that this is what's going on beyond hearsay from your current employer. If your employer took no action (immediately termination) based on this information, the fact that you're gainfully employed despite this false represenation means you'd have a hard time proving much in way of actual damages.
Hope this helps.