Auditory and Visual Threshold Effects of Marihuana in Man: Addendum

Abstract

The figure of 1.312% A~HC for the marihuana used in our investigation (1969) was based on an assay provided by National Institute of Mental Health conducted approximately 2 yr. prior to our use of this substance. Frequent reports by our experienced Ss that the marihuana was of poor quality or low potency caused us to submit samples to two independent laboratories for reanalysis of the heTHC content. We have just recently received these reports, and to our surprise have found the marihuana to be considerably reduced in potency from that originally stated by NIMH (viz., 1.312% ATHC). The report of one laboratory has given a figure of 0.5% ATHC, the other laboratory 0.2%. Furthermore, Dr. Scigliano has communicated to us that the average figure for several subsequent assays of this batch of marihuana by NIMH shows it to contain 1 2% sDTHC. This puzzling discrepancy in potency assay for the same marihuana sample may be explained, in part, by differences in manner of storage between our laboratory and that of NIMH. Upon receipt we stored the marihuana at room temperature, viz., 72'F f. 3'. NIMH has maintained their marihuana in refrigerated storage, and it has recently been stated that marihuana loses its strength if not refrigerated. Furthermore, gas chromatographic techniques for the assay of ATHC are difficult and also standards vary between laboratories. Nevertheless, because the biological end point of drug effect in our investigation was each S's subjective high, our findings may still be considered valid. A note of caution is in order, however, in interpreting our per cent of h9THC obtained in achieving the high. Similar caution is advised in interpreting marihuana research findings where the high is based on providing S with cigarettes of calculated potency based on h9THC assays not of current origin.