What will happen if I ingest dragon dust?

Forgive me if you mean something different, but uming that dragon dust means a dust like debris that is found on the walls of caves of breeding mothers, it likely contains the residue from whatever the dragon used as a fuel for a flame which varies depending on theory. If it is a methane based flame than it wouldn't be too harmful. However, if it is a tail of other volatile substances it could be very poisonous.