26 U.S.C. § 5242

Methanol or other denaturing materials suitable to the use for which the denatured distilled spirits are intended to be withdrawn shall be used for the denaturation of distilled spirits. Denaturing materials shall be such as to render the spirits with which they are admixed unfit for beverage or internal human medicinal use. The character and the quantity of denaturing materials used shall be as prescribed by the Secretary by regulations.