Is stopping cymbalta (duloxetine) after a month dangerous?

Depends. It really depends on for what condition Cymbalta (duloxetine) was prescribed and what was the total dose taken.
If you were on a low. Dose you should be able to stop if since you were on it only one month but it would be in your best interest to call your doctor who is familiar with you and ask their advise on how to stop the medication.