After discussing U.S. obligations to respond to scientific data reported by the U.N. as to the danger presented by a drug or substance, the Controlled Substances Act reserves for the United States the right to have the international legal status of a drug or substance reviewed and amended.

Nothing in the amendments made by the Psychotropic Substances Act of 1978 or the regulations or orders promulgated there under shall be construed to preclude requests by the Secretary of Health and Human Services or the Attorney General through the Secretary of State, pursuant to article 2 or other applicable provisions of the Convention, for review of scheduling decisions under such Convention, based on new or additional information. 21 USC 811(d) (5)

Why would the Secretary of Health and Human Services or the Attorney General make such a request? Most likely because they have discovered information, by way of the official administrative process, that scientific knowledge about a drug or substance has changed. If under U.S. law a substance's status must be changed, then the U.S. is bound by the same law to seek a change in the substance's status under international treaties.