After President Harding and the Senate said no, the League of European stupefacient warmongers limped on without us. So what happened? Here is an excerpt from Prohibition and the Crash by J Henry Phillips
The League of Nations
On the international front the State Department Division of Far Eastern Affairs had approvingly read the Geneva Opium Convention of 1925, and lent a sympathetic ear to the so-called Scheme of Stipulated Supply. The idea was to use futures trading for all legal narcotics procurements. The effect would be to greatly limit production for the illegal market. The World Anti-Narcotic Union had held a gala meeting early in March and obtained verbal support from Governor Al Smith, Mayor Jimmy Walker and Italian dictator Benito Mussolini—but nothing was actually done.
Since 1924 Pennsylvania Congressman Stephen G. Porter had been an influential figure in U.S. drug negotiations with the League of Nations. But the man was a mystical pedant and alienated League members (See and compare A.G. Sessions). Indeed, it was on Porter’s motion that the American delegation to the Geneva conference had petulantly withdrawn from the Convention of 1925. The truth was that delegates from India, Turkey and Persia understood perfectly well that any sudden curbs on opium production would bring on acute economic crises and political instability in their countries. Porter understood none of this and stormed out in a huff, convinced of the foreign delegates’ insincerity. Even before the Great War German chemical interests had struggled against curbs on drugs, and not without reason.
 (Taylor 1969 211, 228) (Eisenlohr 1934 129)
 (NYT 3/8/28 8)
 (Taylor 1969 178-9, 184; 193, 201, 107-8, 213) (Eisenlohr 1934 227, 231, 256-7)