It has been demonstrated experimentally that tolerance to the effects of lysergic acid diethylamide (LSD-25) develops rapidly, both in man1,4,6 and in animals.5 Tolerance to mescaline, with a less rapid development, was observed in rats by Freedman et al.5 We are not aware of studies on tolerance to 2-bromo-d-lysergic acid diethylamide (BOL-148). Tachyphylaxis to LSD-25, it seems, is another problem which has yet to be investigated.
In a previous research3 performed by our group crossed tolerance was demonstrated, in three human subjects, between LSD-25 and mescaline. The purpose of the present study was to confirm our experimental results and to investigate whether rapid tolerance to mescaline also develops in humans, whether subjects having acquired such tolernce are resistant to LSD-25, whether protracted administration of BOL-148 gives a tolerance to this drug and to the chemically related LSD-25, and whether