7 March 1960 Dr, R. Bircher Sandoz Piiarrraceuticals, Inc. Hanovers New Jersey Dear Dr. Bircher: Itle have just finished apreliminar-y assay of the relative potencies of a single dose of LSD-25o 1:,.5 mcg/kg: and of psilocybin., 210 mco/Rg. on 10 new huran'sub32gcls and I thought you might be interested-i'n the results* As the enclosed table sholdsi,.there i,;ere no significant differences with respect to any of the measures eriploy--d (see previous corres-,)ondence for methods), although in 5 of the 7 measures, the effects of LSD-25 uere slightly stronger. This trend, I believe, is due *%.o 2the longer di-,ration of action of LSD@-25, with conseq@uent augr"entation of the differences- hours ,@,raluos ("areas under the curves"). Clinic-ally, there appears to be no real dif,erence between the peak eirfects o.,&" the tivo drugs in these dosageso the similarity zxtending even to the-'@.indidemce of "true" hallueina2tiors and depersonalizatl&or* confirgming Dr. Isbell's observations with lower doses of psilocy,bin. 14e have now commenced the new cross-tolerance study, on 9 subjects,(one dropped out), in which we will use 1.5 ricc3/1"g of LSD-25 and 210 -ric@/,tg of psilocybi.-i as control, test and challenging doses, and increase 2the period of chrdnic into,-ui- cation on each of these drugs to 12 days" Barring unforeseen delays, tiie study shoi-ild be f Lnished by 'i',Iay 10, and I hope that shortly thereafter I will be able to send you a summary of the results. With best personal regards,, Sincerely, Abraham Wikler, 5M.D. Acting Director AW*,bw3 Enclosure 1, -,Y .i 45 210 2 lo) ZIA > 2 1;7 to Cz n t i C,-irt-A r c -i 0 cv, A' f-@ 8 I.A