In 1942, the Supreme Court held that commercial speech was not protected by the First Amendment. Since that time, the Court has adopted the doctrine that the state's concern for the protection of the public is subordinate to the public's right to know. Although the Court has not been unanimous on the issues, the Court has pretty much used the following test to determine whether a particular commercial expression is protected.
Joyce, Walter , "Judicial Scrutiny of Commercial Speech" (1998). Faculty Working Papers. Paper 3.