Can cipro (ciprofloxacin) be effective against an std?

Which STD?: This depends upon which std to which you are referring. It may be effective against some, but certainly not all.

Yes: Ciprofloxacin can be used singly or in combination with other antibiotics for the treatment of gonorrhea, chancroid, and lymphogranuloma venereum. Do not attempt to self diagnose and treat. You should see a clinician for diagnosis and treatment.