From Sefer HaMitzvot (Book of Mitzvot) this mitzvah is #231...
http://www.shemayisrael.com/parsha/chrysler/archives/kisetze71.htmMitzvah 231:
Not to Curse a Fellow-Jew (cont.)
Perhaps one can attribute the fact that a curse is effective to the fact that the Soul of speech stems from the upper realms, as the Pasuk writes in Bereishis (2:7, in connection with the creation of Adam) " … and He breathed into his nostrils a Soul of life and man became a living Soul, 'a spirit that speaks'. G-d therefore endowed the ability to speak with the power to achieve things that are beyond the physical world in which it operates. This explains why we constantly see that, according to the loftiness of the person, and to the extent that he cleaves to spirituality, the words of Tzadikim take effect swiftly regarding the person on whom they pronounce them. This is something that is well-known among people with a deeper perception.
Another reason for the prohibition is in order to prevent discord between one person and the other, but rather to promote peaceful relations between them; since "the birds of the Heaven will carry the voice", and the curse that one utters becomes known to the person concerned, resulting in bad relationships between people.
Whereas the reason given by the Rambam for this prohibition is in order not to elicit revenge and instill anger in the person that one is cursing, since anger is an evil Midah. He elaborates on this point in his Seifer. In any event, he seems to believe that a curse per se, is ineffective, so no harm will befall the person who has been cursed; and the Torah forbids it only because cursing results in anger and revenge.
Some Dinim of the Mitzvah … Although the Gemara in Shavu'os (35a) forbids cursing under any circumstances, someone who does so does not receive Malkos unless he curses using one of the Names of G-d, such as Koh, Shakai, Elokah, or one of His Kinuyin (descriptive Names), such as 'Chanun' or 'Kano' and suchlike. And someone who does is Chayav, irrespective of which language he curses in - including Names of G-d, since any Name of G-d in any language falls under the heading of 'Kinuyin'.