Schedule I is the only category of controlled substances that may not be prescribed by a physician. Under 21 U.S.C. § 812(b), drugs must meet three criteria in order to be placed in Schedule I:
The drug or other substance has a high potential for abuse
The drug or other substance has no currently accepted medical use in treatment in the United States.
There is a lack of accepted safety for use of the drug or other substance under medical supervision.
In 1970, Congress placed marijuana into Schedule I on the advice of Assistant Secretary of Health Roger O. Egeberg. His letter to Harley O. Staggers, Chairman of the House Committee on Interstate and Foreign Commerce, indicates that the classification was intended to be provisional:
Dear Mr. Chairman: In a prior communication, comments requested by your committee on the scientific aspects of the drug classification scheme incorporated in H.R. 18583 were provided. This communication is concerned with the proposed classification of marihuana.
It is presently classed in schedule I(C) along with its active constituents, the tetrahydrocannibinols and other psychotropic drugs.
Some question has been raised whether the use of the plant itself produces "severe psychological or physical dependence" as required by a schedule I or even schedule II criterion. Since there is still a considerable void in our knowledge of the plant and effects of the active drug contained in it, our recommendation is that marihuana be retained within schedule I at least until the completion of certain studies now underway to resolve the issue. If those studies make it appropriate for the Attorney General to change the placement of marihuana to a different schedule, he may do so in accordance with the authority provided under section 201 of the bill. . .
Sincerely yours, (signed) Roger O. Egeberg, M.D.
The reference to "certain studies" is to the then-forthcoming National Commission on Marijuana and Drug Abuse. In 1972, the Commission released a report favoring decriminalization of marijuana. The Richard Nixon administration took no action to implement the recommendation, however. A protracted struggle ensued in which marijuana reform activists began working through all three branches of government to reschedule the drug.