double-edged

adjective2

1. •
   Of a blade, such as a sword or knife, sharp on both edges.
2. •
   (figurative) Beneficial and harmful at the same time; assisting or contributing in one manner while also creating risk or negative consequences.

   • Slander is a double-edged weapon: you can hurt the reputation of another but it diminishes your own reputation that you debase yourself so much.