Variation in the THC content in illicitly imported Cannabis products - Part II




Author: P. B. BAKER,, T. A. GOUGH,, S. I. M. JOHNCOCK,, B. J. TAYLOR, , L. T. WYLES
Pages: 101 to 108
Creation Date: 1982/01/01

Variation in the THC content in illicitly imported Cannabis * products - Part II

Laboratory of the Government Chemist, Cornwall House, London, United Kingdom of Great Britain and Northern Ire/and


The tetrahydrocannabinol (THC) contents of 220 samples of fresh illicit Cannabis products seized on entry into the United Kingdom of Great Britain and Northern Ireland over the period 1979 - 1981 have been determined by gas chromatography. During that period there was a general increase in the quality of both cannabis and cannabis resin, but with wide variations in THC contents both within and between countries. Some very high quality samples of cannabis, cannabis resin and cannabis oil from the Indian sub-continent have been analysed. There have been considerable changes in the number of fresh samples from several countries, compared with the previous survey. Fresh cannabis oil samples were very rare during the period covered by this survey.


In our previous study [ 1] , which covered the years 1975 - 1978, the THC contents of 304 seizures of illicit Cannabis products, as determined by gas chromatography, were reported. This procedure results in the conversion of tetrahydrocannabinolic acid (THCA) to tetrahydrocannabinol (THC) [ 2] , [ 3] and thus measurement of the THC Content of an extract of a sample of a Cannabis product by gas chromatography gives the total amount of THC and THCA present in the sample. Since THCA is also decarboxylated during the smoking process [ 4] , the measurement of "total" THC content provides an indication of the potency of the material to the smoker. In the previous study [ 1] , it was reported that during 1975 and 1976, by far the best quality cannabis originated in South-East Asia (in the form of "Thaisticks"). By 1978, seizures of cannabis from Thailand, while still in the same form, showed a substantial decrease in quality and an increasing seed content. Clarke [5, p. 115] also reported that Thai sticks were originally both of high quality and seedless, but that more recently large quantities of much lower grade Cannabis were being marketed. In our studies, Jamaican cannabis was found to be of considerably higher quality in 1978 than in 1975 - 1976, which may have indicated either a change in selection of materials for export or a change in the plants used to prepare the cannabis. Clarke [5, p. 109] considered that Colombian variants of Cannabis might predominate in Jamaica since the island lies along the smuggling routes between Colombia and the United States of America. That may account for the rise in quality of the Jamaican product.

* Cannabis = Cannabis sativa L.: cannabis = marijuana; cannabis resin = hashish; cannabis oil = liquid cannabis or "hash oil".

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"Street" marijuana in the United States increased markedly in potency between 1975 and 1980, samples rarely exceeding 1 per cent THC in 1975, but samples as high as 5 per cent being common in 1979 [ 6] . No significant rise is observed in the United Kingdom of Great Britain and Northern Ireland over 1975 - 1978 when THC contents for all samples of cannabis are averaged, but if the samples from Thailand are excluded from the 1975 - 1976 figures, a small rise is apparent. Thai seizures over the period were of such high quality and appeared to be both specially prepared and selected that they considerably raised the average THC content of seized cannabis in the United Kingdom (see table 1). However, samples in this and the previous study were all fresh, whereas street samples are by no means all fresh. It could, therefore, be that increase in quality of cannabis in the United States is really an increase in the freshness of the samples rather than an improvement in the stock of Cannabis supplying that market. However, in view of the high quality of cannabis grown in the United States [ 7] and the increasing proportion of that market taken by the home-grown product [ 8] , an alternative explanation could be that the expertise of those growing Cannabis illicitly in the United States is producing a more potent crop.

We now report the results of a survey of the THC Contents of fresh Cannabis products as received in the United Kingdom from a number of countries covering the period 1979 - 1981. Physical and chemical data [9, 10], as well as information from the carrier, were used to assign the country of origin of each sample.


Sample selection

To ensure that the results of the survey would be directly comparable to that previously published [ 1] , only samples which were fresh on arrival in the United Kingdom (i.e. less than three months old) were included in the study. These represented approximately 20 per cent of all samples of illicit Cannabis products submitted to the Laboratory of the Government Chemist, London, over the period 1979 - 1981. In the period covered by the previous survey, approximately 15 per cent of samples submitted were found to be fresh. Prior to analysis, samples were stored in the dark in sealed plastic bags at room temperature.

Sample analysis

Each sample was analysed as received, except that in the case of herbal material, intact stems were first removed. It was necessary to grind resins to ensure complete extraction of the cannabinoids [ 1] . From a minimum of 5 g of a sample (itself representative of the original seizure), 1 g was extracted with methanol (20 ml) by ultrasonic vibration for 20 minutes, a procedure which exhaustively extracts all the cannabinoids. Cannabis oil was warmed and diluted with ethanol to give a solution with a sample concentration of 1 mg/ml. Each extract was analysed by gas chromatography on the same day it was prepared in the manner previously described [ 1] .


The THC content of the cannabis, cannabis resin and cannabis oil seizures is given in tables 2-4. Few countries supplied any appreciable proportion of the total number of fresh samples of the three products. In our previous study [ 1] , the range of values for THC content varied widely even within samples from a given country of origin. This survey has produced a similar result, which was not unexpected since it has been shown that plants grown under identical conditions from the same batch of seeds may have different THC contents [ 11] , [ 12] . Excluding the data for Thai cannabis from the data for 1975 - 1976, the mean THC content of cannabis seizures shows a steady increase over both survey periods, with the 1981 mean twice that of 1975 (see table 1). Fewer fresh samples of Jamaican cannabis were en- countered in 1981 than in any previous year and the overall number of Jamaican seizures fell considerably (see table 5). The two fresh Jamaican samples seized in 1981 were of higher quality than most samples analysed during the 1975 - 1979 period and similar to those analysed in 1980. A similar picture emerged for Nigerian cannabis which increased in quality over the period covered by the two surveys, but where far fewer samples were encountered in 1981 than in previous years. South Africa continues to supply good quality cannabis, the average THC Content in 1981 being higher than in any previous year. Although cannabis from Thailand was not of such overall high quality as in 1975 and 1976 (mean THC Contents 7.8 per cent and 9.3 per cent respectively), there was considerable improvement in the period covered by the second survey from a low value of 3.9 per cent in 1978. However, the overall number of samples dropped considerably during 1979 - 1981. One Thai and one Indian sample analysed in the second survey had THC contents of 12 per cent, a value surpassed only by the highest quality Thai sticks in 1975 - 1978. There has been considerable change in the number of samples, both total and fresh, from many countries; this may indicate a change in trafficking routes or enforcement activities. However, it should be noted that the number of seizures takes no account of their size and there were many seizures in excess of 1000 kg in 1979 - 1981 [ 13] . The data on total number of seizures and the proportion of those which were fresh over the period 1975 - 1981 are given in table 5 for countries supplying significant quantities of Cannabis products to the United Kingdom.

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The THC Content of cannabis resin seizures followed a similar pattern to that of cannabis seizures. Wide variations were found both within and between countries with a slow rise in quality over the period covered by the two surveys (see table 1). There were fewer samples of fresh cannabis resin from Pakistan than in the peak year of 1978, but of generally higher quality. The mean THC Content of cannabis resin from India was high, but with a very large spread of values: two samples in 1981 contained more than 20 per cent THC, the only sample (also from India) in excess of these figures being analysed in 1978 (26 per cent). Only three seizures of fresh cannabis were made from Morocco in 1979 - 1981: A number of large seizures were made from this country over that period and the paucity of fresh material may indicate that large stocks are stored prior to export or that there is an appreciable time between harvesting the Cannabis and processing it into cannabis resin.

Samples of fresh cannabis oils were very rare over the period of this survey: the majority of seizures were of material which was either old or had been prepared from old cannabis or cannabis resin. It may be that such herbs or resins had aged or otherwise deteriorated to such an extent that their sales would have proved difficult on the normal illicit markets and conversion to cannabis oil effectively disguised the poor quality of the original product. One very high quality sample of cannabis oil from India in 1981 contained 70 per cent THC; in view of the high quality of some Indian cannabis resins, an occasional sample with such THC levels is not unexpected. The overall quality of cannabis oils in 1979 - 1981 was not dissimilar to that in the period covered in the previous survey (see table 1).



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A. Ohlsson and others, "Cannabinoid constituents of male and female Cannabis sativa ", Bulletin on Narcotics (United Nations publication), vol. 23, No. 1 (1971), pp. 29 - 32.


P. S. Fetterman and others, "Simple gas-liquid chromatography procedure for determination of cannabinoidic acids in Cannabis sativa ", Experientia, vol. 27, 1971, pp. 988 - 990.


S. Agurell and K. Leander, "Stability, transfer and absorption of cannabinoid constituents of Cannabis (hashish) during smoking", Acta Pharmaceutica Suecica , vol. 8, 1971, pp. 391 - 402.


R. C. Clarke, "Marijuana botany: an advanced study: the propagation and breeding of distinctive Cannabis" (Berkeley, California, And/Or Press, 1981).


"Marijuana and Health", Eighth Annual Report to the United States Congress from the Secretary of Health, Education and Welfare, National Institute on Drug Abuse (Rockville, Maryland, 1980).


J. Flanders, "Sinsemilla harvest", Drug Enforcement (Washington, D. C., Drug Enforcement Agency), vol. 7, No. l (1980), p. 16.


"The US marijuana market", Drug Enforcement (Washington, D. C., Drug Enforcement Agency), vol. 7, No. 1 (1980), p. 36.


M. J. de Faubert Maunder, "The forensic significance of the age and origin of Cannabis", Medicine, Science and the Law , vol. 16, 1976, pp. 78 - 90.


P. B. Baker, T. A. Gough and B. J. Taylor, "Illicitly imported Cannabis products: some physical and chemical features indicative of their origin", Bulletin on Narcotics (United Nations publication), vol. 32, No. 2 (1980), pp. 31 -40.


P. B. Baker, T. A. Gough and B. J. Taylor, "The physical and chemical features of Cannabis plants grown in the United Kingdom from seeds of known origin", Bulletin on Narcotics (United Nations publication), vol. 34, No. 1 (1982), pp. 27 - 36.


P. B. Baker, T. A. Gough and B. J. Taylor, "The physical and chemical features of Cannabis plants grown in the United Kingdom from seeds of known origin, part II, second generation studies", forthcoming.


Report of the Government Chemist 1981 (London, H.M. Stationery Office), forthcoming.