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Dr. R. Bircher Sandoz Pharmaceuticals, Inc. Hanover, New Jersey

Dear Dr. Bircher:

We have Just finished a preliminary assay of the relative potencies of a single dose of LSD-25, 1.5 mcg/kg, and of psilocybin, 210 mcg/kg, on 10 new huran subjects, and 1 thought you might be interested .in the results.

As the enclosed table shows;,there were no significant 1 differences with respect to any of the measures employed (see previous correspondence for methods), although in 5 of the 7 measures, the effects of LSD-25 were slightly stronger. This trend, I believe, is due to the longer duratlon of action of LSD-25, with consequent augmentation of the differenceshours values ("areas under the curves"). Clinically, there appears to be no real difference between the peak effects of the two drugs in these dosages, the similarity axtending even to the:incidence of "true" hallucinations and depersonalizatior, confirming Dr. Isbeil's observations with lower doses of psilocybin.

We have now commenced the new cross-tolerance study, on 9 subjects.(one dropped out), in which we will use 1.5 mcg/kg of LSD-25 and 2i0 mcg/kg of psilocybin as control, test and challenging doses, and increase the period of chronic intoxication on each cf these drugs to 12 days. Barring unforeseen delays, the study should be finished by May 10, and 1 hope that shortiy thereafter i will be able to send you a summary of the results.

With best personal regards,

Sincerely,

Anlibles

Abraham Wikler, M.D. Acting Director

AWtbws

Enclosure

B309

7 March 1960

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Peslixinary Ascay of Relativa Potsncy 10=25, 1.5 mog/kg 7'3a 2alicaybin,210 pez/kg (N = 10)

Pigwrea poprenent moan cifferonces à siandard srrors ef dacserences 1a reccanss 1o a singla deaa 0f Ls0-25 C aad a o pellosybin, ss ond pa. kane or lae difloraness aro

\*, Imdicatos Lsd-25 stranner in sfrect than palloaybia.
-3 Indicatas pellocybin streagor in ofreet than Lcd-d5.

Koter Fop every phyelotogical varicbls ani ia evary sudfeet d5 change jroauced by Lo-25 sad D21 n waro

C3 25

B-308

Slusy 67-C