21 U.S.C. § 903 : US Code - Section 903: Application of State law

      No provision of this subchapter shall be construed as indicating
    an intent on the part of the Congress to occupy the field in which
    that provision operates, including criminal penalties, to the
    exclusion of any State law on the same subject matter which would
    otherwise be within the authority of the State, unless there is a
    positive conflict between that provision of this subchapter and
    that State law so that the two cannot consistently stand together.