Variation in the THC content in illicitly imported Cannabis products

Sections

ABSTRACT
Introduction
Experimental
Results

Details

Author: P. B. BAKER, K. R. BAGON, T. A. GOUGH
Pages: 47 to 54
Creation Date: 1980/01/01

Variation in the THC content in illicitly imported Cannabis * products

P. B. BAKER
Laboratory of the Government Chemist, London, United Kingdom of Great Britain and Northern Ireland K. R. BAGON
Laboratory of the Government Chemist, London, United Kingdom of Great Britain and Northern Ireland T. A. GOUGH
Laboratory of the Government Chemist, London, United Kingdom of Great Britain and Northern Ireland

ABSTRACT

The tetrahydrocannabinol (THC) content of 304 seizures of illicit Cannabis products was determined using gas chromatography. This procedure results in the conversion of THC acid to THC itself and thus gives the total THC content of the material, which reflects its potency as experienced by the smoker. The study was carried out over three years, thus enabling comparisons to be made between THC levels from a given country of origin over this time span in addition to any variations between the countries. In the early part of the study, herbal cannabis from South East Asia was consistently the best quality and that from the Caribbean the poorest quality. In the third year of the study, the material from South East Asia was in general no richer in THC than material from other areas of the world. Cannabis resins normally had higher THC contents than most herbal material, but the highest levels were found in "hash oil" from the Middle East and the Indian subcontinent.

Introduction

The price of Cannabis products on the illicit market is governed inter alia by their quality as perceived by the user. It has been established for some years that the major psychoactive constituent in Cannabis is Δ 9-tetrahydrocannabinol (THC) and the level of this compound in Cannabis products can therefore be used as a guide to quality.

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

The major cannabinoids (THC, cannabinol and cannabidiol) can be separated by thin-layer chromatography. Quantitative information can be obtained by making absorption measurements after reacting the separated constituents with azo dyes. Using this method Nielsen [ 1] examined cannabis grown in Denmark and found that the THC content of the dried mature plant varied between 0.04 and 1.7 per cent. The majority of reports describe the use of gas chromatography to separate the cannabinoids, and quantitative information is based on measurements using the flame-ionization detector. Quantitation has been carried out using either internal or external standards with coefficients of variation ranging from 1 to 3 per cent, which is adequate for the present work [ 2] - [ 6] . Reviews of gas chromatographic procedures have been published [ 7] , [ 8] in which various stationary phases and operating conditions have been compared. Satisfactory separation of cannabinoids, after extraction, may be obtained using a variety of silicone gum phases. It has, however, been noted that loss of THC by absorption on stationary phases can occur at low THC levels [ 9] .

A method has also been described in which the direct injection of solid cannabis is made [ 10] . However, there is ample evidence to show that the cannabinoid content varies within a plant [ 11] . This method has therefore no advantage over extraction procedures as in order to obtain representative and homogeneous samples a large amount must be prepared from which an aliquot is taken. Ohlsson et al. [ 12] have shown that there is no significant difference between the THC levels (and between other cannabinoid levels) in male and female plants grown under the same conditions. We have, however, noticed that the majority of herbal sample seizures submitted to us do not contain a significant proportion of male plants.

The cannabinoid acids are thermally labile and the use of gas chromatography results in their decarboxylation to the corresponding cannabinoids. Quantitative measurement of the THC content by gas chromatography therefore gives the total amount of THC and its acid (THCA), the latter being quantitatively converted to THC on injection [ 12] , [ 13] . For the present study this is an advantage because the acids also decarboxylate during the process of smoking. It is possible to determine the THC and THCA content separately by gas chromatography using derivatization [ 14] , [ 15] or selective extraction [ 16] , although recent developments enable this to be done more readily using high-performance liquid chromatography [ 15] , [ 17] , [ 18] . There have been reports of the conversion of cannabidiol (CBD) to THC, or a compound of the same gas chromatographic retention time, and this could give rise to erroneous THC levels using gas chromatography [ 19] . Under the conditions used in the present work this conversion was not observed. Changes in the THC content during the growth of the plant have been studied and seasonal variations in THC content have been noted [ 3] , [ 20] . The THC content of harvested material decreases on storage and there have been several studies in which plant material from a single plant has been stored under different conditions to determine the effects of temperature, light and air on changes in cannabinoid levels [ 11] , [ 21] . Even after solvent extraction, cannabinoid concentrations will still change and analysis should be carried out as soon as possible after preparation of the extract [ 22] , [ 23] .

There are several reports in the literature on the THC content of cannabis and these are summarized in table 1. In the present context the origin refers to the country in which the plant was grown and not the country of origin of the seeds. It should be noted that, although all the THC levels quoted are expressed as a percentage of dry weight of cannabis, it is not clear in all cases whether any selection of plant material had taken place. In all but one study, values were obtained by gas chromatography and therefore include THCA. As far as can be ascertained, samples were extracted and analysed within a short space of time so that the effects of sample or extract storage on the THC levels was minimal [ 24] . Most of the data in table 1 are derived from cannabis legitimately grown and processed as part of scientific studies on cannabinoids. In contrast, the present work is concerned with the THC content of illicit supplies of Cannabis products and all samples have been taken from seizures by law enforcement agencies in the United Kingdom. Jenkins and Patterson [ 25] have extensively studied illicit Cannabis products, but the data are expressed in terms of the relative proportions of THC, CBD and cannabinol (CBN) rather than their concentrations in the plant. The valuable study by Marshman et al. [ 20] is restricted to Jamaican cannabis. The origins of the samples analysed by Eskes et al. [ 26] , all of which were seizures, are not quoted.

Table 1

Summary of published data on THC content of mature cannabis

 

THC content(%)

 

Number of samples/plants examined

Country of growth

Range

Mean

Reference

13/13
Argentina
0.1 - 8.3
2.2 [5]
8/2
Brazil
0.7 - 2.5
1.5 [31]
15/unknown
Canada
0.02- 3.5
...
[34]
10/10
Costa Rica
1.0 - 3.7
1.8 [33]
21/12
Denmark
0.04- 1.7
0.6 [1]
72/36
Jamaica
0.04- 7.9
2.8 [20]
60/30
Jamaica
0.7 -10.5
2.9 [30]
32/8
Lebanon
0.01- 1.2
0.27 [12]
13/13
Mexico
0.1 - 3.0
1.7 [33]
27/8
Sweden
0.00- 0.4
0.04 [12]
49/12
United Kingdom
0.02- 7.1
2.0 [32]
30/30
United States
0.1 - 0.5
...
[3]
120/120
United States
0.04- 6.1
1.3 [33]
40/unknown
Unknown
2.2 -10.3
4.4 [26]
68/unknown
Unknown
0.02- 3.5
...
[34]

We now report the findings of a study of the THC content of cannabis, resin and oil as received in the United Kingdom from a number of different countries over three one-year periods. The most probable country of origin was assigned by taking into account information from the carrier, visual appearance [ 27] , and the thin-layer and high-performance liquid chromatographic characteristics [18, 28]. For completeness, the data for 1975 for cannabis and resin which have been published in the Report of the Government Chemist 1976 [ 29] have been included.

Experimental

Sample selection

Only samples which to the best of our knowledge were fresh (i.e. less than three months old) on arrival in the United Kingdom were included in the study. This represents approximately 15 per cent of all illicit Cannabis samples submitted to the laboratory over the same period of time. Most samples were analysed within one month of seizure, during which time they were stored in sealed plastic bags at room temperature. Each seizure was analysed as received, except that in the case of herbal material intact stems were first removed. Resin (5 g) or herbal material (2.5 g) was subjected to Soxhlet extraction using 100 ml of ethanol (PBS grade) and the optimum extraction time was found to lie between 60 and 90 minutes. Excessive time resulted in loss of THC by thermal degradation and too short a time in incomplete extraction. It was necessary to grind the resin prior to extraction in order to recover all the THC. For example, two samples of the same resin, one untreated and the other ground, gave THC values of 2.4 and 4.6 per cent, respectively, when extracted for the same time. Examination of the final extract was made on all samples to ensure that extraction was complete, and in no case was any THC found.

Reproducibility of extraction was measured using nine samples of herbal material from a single seizure and results were sensibly constant. It is known from other studies [ 18] that in resin, at least from Pakistan and Lebanon, the cannabinoids are uniformly distributed within a block.

Liquid cannabis ("hash oil"), which varied in viscosity from a freely flowing liquid to almost solid, was warmed and diluted with ethanol to give a 1 mg/ml solution.

Analysis of extract

Each extract, which was analysed on the same day that it was prepared, was made up to 200 ml in ethanol, a 1-ml aliquot was diluted to 10 ml and 5μl of this solution analysed by gas chromatography. A Pye-Unicam model 104 instrument was fitted with a 1.5 m x 4 mm internal diameter glass column containing 3 per cent OV17 stationary phase on 100-120 mesh Gaschrom Q support. The carrier-gas flow rate was 30 ml/min and the column temperature was 250°C. Detection was by flame ionization and the detector was calibrated for THC response using a primary standard of 0.01 per cent THC in ethanol.

Results

The THC content of plant material, resin and hash oil seizures are given in tables 2-4. For some countries there were very few samples, but it is apparent that the range of THC content varies widely even from a given country of origin. This is to be expected, since even plants grown under carefully controlled conditions show wide variations in THC content (see table 1). However, the quality of cannabis from some areas is consistently better than others. During 1975 and 1976, Ghana yielded cannabis low in THC compared with other African countries, but the samples seen in 1978 were of better quality. Jamaican cannabis was consistently poor in 1975 and 1976 and no material high in THC, such as obtained by other workers from dealers in Jamaica [ 20] , was found in the United Kingdom. By contrast, there was a noticeable improvement in the Jamaican material in the third year of the study. Mean values for all samples in the present study were, however, little different from published mean values [ 20] , [ 30] .

Table 2

Total THC content of seized cannabis

 

1975 THC content (%)

 

1976 THC content (%)

 

1978 THC content (%)

Country or area of origin

Number of samples

Range

Mean

Number of samples

Range

Mean

Number of samples

Range

Mean

Bangladesh
5
1.4- 4.4
3.0
-
   
-
   
Colombia
-
   
-
    3
2.5- 3.9
3.4
Ghana
7
0.7- 2.5
1.6 9
0.4- 2.8
1.3 6
1.4- 3.4
2.4
India
-
    1 2.7 2.7 4
1.7- 7.8
5.5
Jamaica
16
0.2- 2.7
1.8 9
0.7- 3.3
1.9 15
1.5- 5.0
3.7
Kenya
1 2.7 2.7 6
1.0- 4.2
2.2 13
1.0- 3.9
2.2
Morocco
-
   
-
    2
0.9- 1.3
1.1
Nigeria
2
2.0- 2.8
2.4 5
0.8- 5.9
3.4 16
2.3- 7.4
4.1
South Africa
5
2.3- 6.3
4.1 5
0.6- 2.8
2.6 8
2.3- 5.5
3.6
Southern Rhodesia
-
   
-
    2
2.7-12
7.3
Swaziland
2
2.1- 2.4
2.3
-
   
-
   
Thailand
10
3.8-17
7.8 11
5.1-17
9.3 13
0.4- 8.8
3.9
Zambia
2
2.2- 2.7
2.5 4
2.6- 4.1
3.9 4
1.3- 4.0
2.3
Total
50     50     86    

Table 3

Total THC content of seized cannabis resin

 

1975 THC content (%)

 

1976 THC content (%)

 

1978 THC content (%)

Country of origin

Number of samples

Range

Mean

Number of samples

Range

Mean

Number of samples

Range

Mean

India
-
    1 3.5 3.5 11
2.2-26
11
Iran
2
1.5- 2.7
2.1
-
   
-
   
Lebanon
-
    10
2.2- 8.0
4.4 3
1.0- 8.5
4.3
Morocco
6
4.0-16
9.5 2
3.8- 9.4
6.6 7
4.7- 9.2
7.4
Nepal
-
    2 14 14 2 11 11
Pakistan
3
2.5- 7.3
4.6 5
3.9-12
7.2 19
3.2-16
6.2
Turkey
-
   
-
    4
8.8-13
10
Total
11     20     46    

Table 4

Total THC content of seized "hash oil"

 

1975 THC content (%)

 

1976 THC content (%)

 

1978 THC content (%)

Country of origin

Number of samples

Range

Mean

Number of samples

Range

Mean

Number of samples

Range

Mean

India
5
20-48
33 1 40 40      
Kenya
2
28-39
34
-
         
Lebanon
-
    2 16 16      
Morocco
-
    8
2-18
8.5      
Pakistan
12
25-42
30 11
13-29
18      
Total
19     22          

In the same two years, by far the highest quality cannabis originated in South East Asia (exclusively in the form of "Thai sticks") and this was reflected in its street price, at least in the United Kingdom, over the same period. However, the 1978 seizures which originated in Thailand, while still prepared in the form of sticks, showed a dramatic decrease in THC level compared with previous years. A careful study of the physical appearance of seizures of Thai origin for the three years revealed an increasing seed content in the cannabis. It is not possible to examine the data for any correlation of THC content with season because our procedure for estimating age will not discriminate between differences of less than three months and because there were, in most cases, insufficient samples upon which to base any such conclusion.

The cannabis resins generally had a higher THC content than most of the herbal material with the exception of the best Indian, Rhodesian and Thai material. For any given country there was a wide range of THC values. Not surprisingly, the highest levels of THC were encountered in the hash oil seizures, with values as high as 40 per cent. A comparison of the mean amounts of THC in cannabis resin and hash oil from the same countries (tables 3 and 4) shows that for India, Lebanon and Pakistan, the oil contains approximately three times the amount present in the resin. By contrast, Moroccan oil, which is the least viscous encountered, has no more THC than resin from the same country.

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020

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