An oral preparation for promoting expression of TGF-&bgr； includes as an active ingredient hyaluronic acid or a pharmaceutically acceptable salt thereof, the oral preparation promoting expression of TGF-&bgr； in plasma. In addition, an oral preparation for suppressing production of a pain-producing substance includes as an active ingredient hyaluronic acid or a pharmaceutically acceptable salt thereof, the oral preparation suppressing production of a pain-producing substance by promoting expression of TGF-&bgr； in plasma. In addition, an oral preparation for suppressing production of a pain-producing substance includes as an active ingredient hyaluronic acid or a pharmaceutically acceptable salt thereof, the oral preparation suppressing production of a pain-producing substance PGE2 and/or bradykinin. In addition, an oral preparation for suppressing edema includes as an active ingredient hyaluronic acid or a pharmaceutically acceptable salt thereof, the oral preparation suppressing production of a pain-producing substance PGE2 and/or bradykinin.
