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CROSS TOLERANCE BETWEEN LSD-25 AND PSILOCYBIN.

Recently It has been shown (Hofmann st nl, 1958a; Isbel1, 1959) that 0-Phosphoryl-4-hydroxy-H-dimathyl tryptamine (hereafter refcrred to as psilocybin), a compound isolated from certain species of mushrooma (Hofmunn st al, 1958b) which are used ceremonially by Mexican Indians (Wasson and Vasson, 1957), has paychotoaimetic properties very similar to those of LSD-25. The close resenblance of the pattorns of sysptoms induced by LSD and pailocybia suggested that thess druçs cause a poychosis by some comaon biocheaical or physiological mechanisa. Sincs the sffects of LSD diminiah rapidly when the drug Is given dnily (Isbell et nl, 1956), it was felt that the hypothesis that tha LSD and psllocybin psychoses are identical could be tested by determining If cross-tolerance existed between the two drugs. In other words, if the degres of tha reactioa induced by a given dosà of psilocybin was significantly less in a person made tolerant to LSD, cross tolerancs would be said to exist, and, converseiy, tha reaction to a given dose of LSD ahould be reduced in a person talerant to psllocybin. In the latter case, it is implied that tolerancs to pailocybin would develop.

19 kay 1959

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METHODS

Sudleats, Five male formar opiate addicts who wero serving sentences for violation of the U. S. narcotic laws voiuntcered for the expariments. Their ages varled betweon, 25 and 35 ycars. A1l were physically healthy and none presented any svidence of the major psychoses. All had received LSD-25 in previcus experiments.

General Conditions. The subjects were housed In a spccial ward devoted to clinical research. Teoperatures, respiratory rates and blcod pressures were measured three tiaes daily after the patients had restsd quietiy in bed during days in which special moasurenents were not being made. The patients ware observed bs specially trained aides with long experience in. detacting drug-induced chenges in behavior.

Prugs. The deslgn of the experiment is sumnarized in Tabls i. LSD and psilocyhin were given in 30 ce of cherry syrup at 8 a.m. with the patients fasting. All doses wers calculated on a mcg/kg basis. Control exparinents were carried out, using 1.5 mcg/kg ef LsD, 150 meg/kg of psilocybin and a placcbo, before the firat period of chronie intoxication and after the period of placabo medication prior to the second period of intoxication. Control tests with LsD and psilocybia vere

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conducted at least five days apart in order to prevent the developusnt of tolsrancs. The order of administration of placebos, LsD and pellocybin was randonized in both control periods.

Thore were two perlods of chronic drug administration -- cne with LsD and ona with psilocybin. Ths order in which the 5 patients recaived the drugs chronically (first or second) was randomlzed, with 3 recelving LsD first and 2 receiving poiiocybin first. Aftsr the necessary measurements had been obtalned, LsD or psilocybia vas replaced with placebos for at leust seven days, after which the sscond controls wera obtained. Folloaing this placebo period, those patients who had received LSD chrontcally received psilocybin chronically, end viee versa.

The doaes of LSD end psilocybin on the first day of chronic intoxication were 0.25 mog/kg and 25 mcg/kg respectively. These doses were increased by 0.25 mcg/kg (LSD) or 25 mcg/kg (psilocybin) on each succseding day until 1.5 mcg/kg of LsD or 150 mcg/ka of psilocybin were being givan on the sixth day. On the eighth or ninth day of chronic edainistration detailed measurenents were made aftor administration of the drug which the patient had been recciving chronically. Thia served as a

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test of "direct" tolerance to that drug. On the subsequent day, the paticnt was "challenged" with the drug (l.5 mcg of L5D or 150 mcg of psilocybin) that he had not beea receiving. This served as a tast of "cross" tolsrance.

The pattents were then plsced on placehos for 7-l0 days after which they were tested again with placebo, 1.5 mcg/kg of LSD, snd 150 meg/kg of psilocybin. Thase "second controls" ware obtained to detarmine if toleraace had baen lost.

The patlents wers then returned to chronic madication folloving ths schedule described abovs, with thoss petlents who received LSD in the first period of chroaic adainistration now being given psilocybin, and vics versa. The patients were then challenged with LsD and psilocybin in the manner descrlbed above.

Observations. Durlag each day of the control pertods and the periods of chronic drug adninistration during which the patients were "challcaged" with piacedo, LSD or psilocybia the following observations were mads at hourly intervals twice before and eight tizes after adainistration of the druga: rectal teaperature, pulse rate, systolic blood pressure, pupillary size, and threshold for elicitation of the kneejerk.

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The methods used wre those prsviously described (lobell ot al, 1956; isbell et nl, 1959; Isbell, 1959). In adaltion the patlonts completed, with the help of an alde, a special questionnaire at hourly intervals from 7:30 a.m. to 3:30 p.m. At these saas times, general notes on behavior were uritten. 2 Clinical grades of the intensity of the reaction were assignod on the basis of the syaten of Isbeli et.2l (1956).

Analysis of Data. After drug adainistratlon the change in rectal temperature, pulse and respiratory.rates, pupillary size, biood pressurs and thrsshold for elicitation of the knesjerks vere calculated by subtracting the averaga of the two pre-drug obssrvations from the values obtained at various hours. The areas under the tina-action curves for cach particular seasurement composed of these figures were calculated by the mathod of winter ana Flataker (195o), thus converting all the data on a particular subject, a particuiar drug and a particuler day to one figurs termed "degres-hours" (teoperature), "beat-hours" (pulss rate), etc. The total number of positive reaponses on the questionnaire were counted over the entire period, eliminating answors vhich wera also scored positively before the drug. Means and standard errora of means were cniculated according to standard statistical techniques.

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Tha diffsrences in tho various measurements after piacebo, 1.5 mog/kg of LSD, and 150 mog/kg of psilocybin in the first and second contrcl periods were cvaluated by a t-test for paired observations (Edwards, 19hé). Since none of the differences were statistically significant in the two sets of controls, they were averaged and the averages used in evaluating the presencs and degres of toleranee, and cross-tolerance.

Ths differences in the effeçt or LSD and psllocybin after chronic adminlstratlon of LSD and psilocybin were then evaluated by the sase statistical technique for differances in paired observations. Four coaparisons were madet (1) response to LsD after chronie administration of LSD (direct tolerance to LSD); (2) response to psilocybin after chronlc administration of LSD (cross tolerance LSD and psilocybin); (3) response to psilocybin after chronie adqinistration of psllocybin (direct tolorance to psllocybin); and (h) responss to LSD efter chronic adainistration of psitocybin (cross tolerance psilocybin and LSD). Tha signs of the differenceo were so arranged that a miaus (-) sign indicated a dscrease in the measurement after chronic intoxication as compared with control, and a plus (+) sign lndicated an Incrsese.

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RESULTS

The differences between the first and second controls are shown in Table 2. None of the differences are statistically significant, as indicated by the large standard errors. There dld seen to be a tendençy for the messurements of pulse rate, biood prsssure, and threshold for the knesjerk to decreese on the second control. A slight dacrease in the nuaber of positive responses on the second control also occurred with both LsO and psilocvbin,These decreases pay possibly Indicate that scae degree of residual tolerance and cross tolerance was present even after a weekts tine.

The diffarences in the rasponses to LSD and psilocybin after chronic administration or either drug are shown in Table 3. The first column shows the response to LSD after chronic adainiotration of LSD, and reflects direct tolerance to LSD. The second column shows the response to psilocybin after chronic trsatzent with LsD, and reflects "cross" tolerance between LSD and psiloeybin. The third coluen shows tho response to LSD after chronic administration of psilocybin, and is a-meusure of crass tolerance between LSD and pailocybin. The last (fourth) coluan shows the response to psilocybin after chronic treatment with psilocybin, and is a nessure of cirèct tolerance to psilocybin.

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Inspoction of the tabie shows that ali tha signs were minus signs, which seggests ths presence of tolcranca and cross tolorance to bothdruns. In the case of direct tolerancs (first colunn) to LSD, tha changes were highiy significant statistically (P <0.01) on three meesuraa (blaod préssure, pupiilary'size, and clinical grade) and significant (P <0.05) on ons measure (pulse rate). In the cass of direct tolerance to psilocybin (fourth coluam), highiy significant dacreases pers obsorved in threshold for tha kmeejerk, and on clinical grade. A significant change ia the puisa rate was also seen. In the cass of crosa tolerance between LSD and psflocybin, a highiy significant dacrease was observed in the threshold for the kneejsrk, and significant decreases varo seen on blood pressure, pupillary sise and ciinical grade. Tha results are not as cicar in case of cross toleranca batween psilocybin and LSD (coluan 3). Although the responses were less on all measures, the changes were significant only in the cases of the blood pressuro and clinical grade.

Ths data leave llttle doubt that a great deal of direct tolerancs to LSD was inducad, and that, whila ths patients vers tolorant to LSD, considerable cross toleranco ta psilocybin was present. In ths case of direct tolerance to psilocybin,

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interpretation is not as easy. Although ali the changes were in the proper direetion, and, ln the cass of two of the measurenents, highly significant, ths megnitude of the decrease in the responsss was less than with direet tolerance to LSD. These facts suggest.that, although tolerance to psilocyhin doss dovelop, it davelops moza'slowiy or is less complete than is tolerance to LSD. Por this reason, the rciatively snall (though consistent) declins in the response to LSD after chronic treatosnt vith,psilocybin is not surprising.

The failure to reach sigaiflcancs in the decreass in respoases on the questionnairo wes due in every case to one incividual who was very sensitive to both drugs sdila not toleraat. He scored over 200 responses after LSD, and over 90 responses after pallocybin in both the first and second controls. The naber of responses on challenge with either LSD or poilocybin sfter chronic adainistrution of either drug varied batween 10 and 30. The decrease in the nuaber of positiva responses was. thorefore, vary great and indicative of a high degree of tolerance and cross tolerance, Ths large size of ths differonce, for the group as a whole however, skewed the distribution of the data/and sads the variance vory larqe, and therefore pravented a statisticaily significant result.

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. Since ths expsriment was not entirely conclusive, and since the fallura to reach s completely conclusive result aight be dua to the small nuaber of subjects, it should be repeated using the sane design in the hope that the large number of subjects wili reduce the varlance. It is aiso possible that tha failurs to reach statistical sigaificance was due to a relatively low degree of tolerance to psllocybin. In the latter case, the peried of. chronic treatzant with psilocybin shodld be extended and, perhaps the patlocybin dosage ehculd be increased to 200 mcg/kg.

Although not entirely conclusiva, the resuits are sufficiently suggestive to support rathar strongly the notion that LSD and psliccybin induce a psychosis by some common blocheaical or physiological mechanism.

SULMARY

1, Cross toleranca-between LSD-25 and psilocybin was tested by "challengiag" 5 nen with 150 acg/kg of pallocybin after they had received LsD-25 oncs daily for 7-8 days (25 mon/kg inorgasing to 150 meg/kg).

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2. A high degree of "direct" toierance developed to LSD after chronic adainistration for 7-8 deys. The development or "direct" tolerance to psilocybin was not proved conclustvely, aithough tho results are strongiy suggestive that partial toleronce to pallocybin was present.

3. Responses to psilocybin after chronic adainistratlon of LSD ars highly suggeotive of cross tolerance detween LSD and psllocybin. Dinimution in the responses to LSD after chronic trsataent with psilccybin, whiia suggestive,.were not sufficlently great to establish concluslvely the presance of cross tolerance between psllocybin and LSD.

h. The experiment shouid be extended to includs at lsast 5 other subjects and, if the results are still inconcluslve, LSD and psliocybin shouid be extended fer a longer periot of tims and higher doses glven.

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REFERENCES

EDVARDS, A. L.: Statisticsl Analysis for Students in Peychology end Educatton, 1. New York: Rhinehart and Co., 19hó.

HOFMANN, A. R., HEIM, R., BRACK, A., and ROBEL, H.: Psilocybin, ein psychotroper Wirkstaff and dem Mexikanichen Rauschpilz, Pallccrbe Hexicana Heia. Exaeriantia (Bascl) 14: 107 (1958a).

HOFMANL, A., FREY, A., OTT, H., PETRZILRA, H., and TROXLER, F.r Ronstitutionsaufklarung uad Synthese von Fsilocybin. Experiantia (Basel) 1h: 397 (1958b).

ISBELL, H.i Coaparison of the reactions induced by psilocybin and LsD-25 in man. Pavchopharancolonia, in press (1959).

ISBELL, H.,BELLEVILLE, R. E., FRASER, H. F., WIKLER, A. and LOGAN, C. R.: Studies on lysorgic acid diethylaaide (LSD-25). I. Efreots in foraer morphine addicts and development of tolerance during chronic intoxication. A.M.A. Arch. Neurol. 6 Psvchlat., 76s 465-478 (1956).

ISBELL, H., LOGAN, C. R., and MINER, E. J.1 Studies on lysergic ecid diethylamide (LSD-25). IIl. Attempts to attenuatc the LSD-reaction in man by pretreatment with neurohumoral blocking agenta. A.M.A. Arch. Hleurol. & Pavchiat., 81: 20-27 (1959).

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WASSON, V. P. and WASSON, R. G.t Mushrooms, Russla and History. Naw Yorkt Pantheon Books, 1957.

WINTER, C, A. and FLATARER, L.t Studies on Heptazone (6=Morpholino-4,4-dipheny1-3-heptanone hydrochloride) in comparison with other analgesic agents. J. Pharmacoi. & Exper. Thora2., 96: 305-317 (March) 1950.

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FOOTHOTE 1.

Footnots l. We are indebted to Drs. R. Biroher and C. Hicnse of Sandoz Pharmaceuticals, Hanover, N. J. for supplies of psllocybia and LSD.

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ExperImental Deslgn for Testing Cross-roicranee

t. Subjects "y" first rsceived LsD chronicaliy.

2. Subjects "Y" recelved psilocybin Hrst.

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Table 2.

Differences in Rssponses to Placcbo, 1.5 mog/kg ef LSD-25, and 150 mcg/kg of Psilocydin on First and Second Controls.

Figures represant the mean differences à otandard crrors of the differonces hetwoen seasuremants on the first and second controls in 5 aubjects. None of ths differences are slgaificant.

, Indicates that the average measurement tas inereased on the sscond contral;

-, Indicates that It decreased.

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Table 3.