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7. The psychological effects of chronic cannabis use
7.2 Psychological adjustment in adults
7.2.1 Is there an amotivational syndrome?
Anecdotal reports that chronic heavy cannabis use impairs motivation and social performance have been described in the older literature on cannabis use in societies with a long history of use, such as Egypt, the Carribean and elsewhere (e.g. Brill and Nahas, 1984). In these societies, heavy cannabis use is the prerogative of the poor, impoverished and unemployed. With the increase of cannabis use among young adults in the USA in the early 1970s, there were clinical reports of a similar syndrome occurring among heavy cannabis users (e.g. Kolansky and Moore, 1971; Millman and Sbriglio, 1986; Tennant and Groesbeck, 1972). These investigators have typically described a state among chronic, heavy cannabis users in which the users' focus of interest narrowed, they became apathetic, withdrawn, lethargic, unmotivated, and showed evidence of impaired memory, concentration and judgment (Brill and Nahas, 1984; McGlothin and West, 1968). This constellation of symptoms has been described as an "amotivational syndrome" (e.g. McGlothin and West, 1968; Smith, 1968), which some have claimed is an organic brain syndrome caused by the effects of chronic cannabis intoxication (Tennant and Groesbeck, 1972). All these reports have been uncontrolled, and often poorly documented, so that it has not been possible to disentangle the effects of chronic cannabis use from those of poverty and low socioeconomic status, or pre-existing personality and other psychiatric disorders (Edwards, 1976; Millman and Sbriglio, 1986; National Academy of Science, 1982; Negrete, 1983).
There is no research evidence which unequivocally demonstrates that cannabis does or does not adversely affect the motivation of chronic heavy adult cannabis users. It has proved singularly difficult to provide better controlled research evidence which has permitted a consensus to emerge upon the issue. Two types of investigation have been carried out in an attempt to assess the motivational effects of chronic heavy cannabis use: field studies of chronic heavy cannabis using adults in societies with a tradition of such use, e.g. Costa Rica (Carter et al, 1980) and Jamaica (Rubin and Comitas, 1975); and laboratory studies of the effects on the motivation and performance of volunteers who have been administered heavy doses of cannabis over periods of up to 21 days (e.g. Mendelson et al, 1974). There has also been some evidence on the prevalence of adverse psychological effects of cannabis from a small number of studies of chronic cannabis users (e.g. Halikas et al, 1982).
7.2.2 Field studies of motivation and performance
Rubin and Comitas (1975) examined the effects of ganja smoking on the performance of Jamaican farmers who regularly smoked cannabis in the belief that it enhanced their physical energy and work productivity. They used videotapes to measure movement and biochemical measures of exhaled breath to assess caloric expenditure before and after ganja smoking. Four case histories were reported which indicated that the level of physical activity increased immediately after smoking ganja, as did caloric expenditure, but not productivity. It seemed to be that after smoking ganja the workers engaged in more intense and concentrated labour, but this was done less efficiently, especially by heavy users. Contrary to the hypothesis that cannabis use produced an impairment in motivation, they concluded: "In all Jamaican settings observed, the workers are motivated to carry out difficult tasks with no decrease in heavy physical exertion, and their [mistaken] perception of increased output is a significant factor in bolstering their motivation to work." (p79).
A study of Costa Rican cannabis smokers produced mixed evidence on the impact of chronic cannabis use on job performance (Carter et al, 1980). A comparison was made of the employment histories of 41 pairs of heavy users (10 marijuana cigarettes per day for 10 or more years) and non-users who had been matched on age, marital status, education, occupation, and alcohol and tobacco consumption. The comparison indicated that non-users were more likely than users to have attained a stable employment history, to have received promotions and raises, and to be in full-time employment. Users were also more likely to spend all or more than their incomes, and to be in debt. Among users, however, the relationship between average daily marijuana consumption and employment was the obverse of what the amotivational hypothesis would predict, that is, those "who had steady jobs or who were self-employed were smoking more than twice as many marijuana cigarettes per day as those with more frequent job changes, or those who were chronically unemployed" (p153), indicating that "the level of consumption was related more to relative access than to individual preference" (p154).
Evidence from these field studies is usually interpreted as failing to demonstrate the existence of the amotivational syndrome (e.g. Dornbush, 1974; Hollister, 1986; Negrete, 1988). There are critics, however, who raise doubts about how convincing such apparently negative evidence is. Cohen (1982), for example, has argued that the chronic users in three field studies have come from socially marginal groups, so that the cognitive and motivational demands of their everyday lives were insufficient to detect any impairment caused by chronic cannabis use. Moreover, the sample sizes of these studies have been too small to exclude the possibility of an effect occurring among a minority of heavy users.
Other evidence suggests that an amotivational syndrome is likely to be a rare occurrence, if it exists. Halikas et al (1982), for example, followed up 100 regular cannabis users six to eight years after initially recruiting them and asked them about the experience of symptoms suggestive of an amotivational syndrome. They found only three individuals who had ever experienced such a cluster of symptoms in the absence of significant symptoms of depression. These individuals were not distinguished from the other smokers by their heaviness of use. Nor was their experience of these symptoms obviously related to changes in pattern of use; they seemed to come and go independently of continued heavy cannabis use.
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7.2.3 Laboratory studies of motivation and performance
In the light of Halikas et al's low estimate of the prevalence of amotivational symptoms among chronic heavy cannabis users, it is perhaps not surprising that the small number of laboratory studies of long-term heavy cannabis use have failed to provide unequivocal evidence of impaired motivation (Edwards, 1976). The early studies conducted as part of the LaGuardia Commission inquiry (see Mendelson et al, 1974) reported deterioration in behaviour among prisoners given daily doses of cannabis over a period of some weeks, but these reports were based upon largely uncontrolled observation. So too was the more recent study of Georgotas and Zeidenberg (1979) in which it was reported that five healthy male marijuana users who were placed on a dose regimen of 210mg of THC per day for a month appeared "moderately depressed, apathetic, at times dull and alienated from their environment and with impaired concentration" (p430).
A study which used standardised measures of performance rather than relying on observational data failed to observe such effects (Mendelson et al, 1974). In this study 10 casual and 10 heavy cannabis smokers were observed over a 31 days study period in a research laboratory. For 21 of these days, subjects were given access to as many marijuana cigarettes as they earned by performing a simple operant task which involved pressing a button to move a counter. The points could be exchanged for money (60 points equal to a cent), packets of cigarettes (3,000 each), and marijuana cigarettes (6,000 each). Mendelson et al found that all subjects earned the maximum number of points allowed per day (60,000) throughout the study and hat output was unaffected by marijuana smoking whereas ad libitum access to alcohol by heavy drinking subjects in the same setting profoundly disrupted performance of the same task. Mendelson et al concluded that: "our data disclosed no indication of a relationship between decrease in motivation to work at an operant task and acute or repeat dose effects of marihuana" (p176).
A number of criticisms can be made of this study. First, the period of heavy use was only 21 days by comparison with the life histories of 15 or more years daily use in heavy cannabis users in the field studies. Second, the subjects in the study were volunteers who were all healthy, young cannabis users with a mean IQ of 120 and nearly three years of college education, and some of whom reported during debriefing that they were motivated to perform well so as to demonstrate that their cannabis use did not have any adverse effect on their performance (Mendelson et al, 1974). Third, the tasks that users were asked to perform (button presses) were undemanding. Mendelson et al countered that these tasks had nonetheless been shown to detect the deleterious effects of heavy alcohol use. Moreover, they argued, there were other indicators that their subjects' performance and motivation was unimpaired while using cannabis, namely, all subjects completed the study, most undertook the daily assessments conducted throughout, all complied with a roster for cleaning and house-keeping duties, and all kept up their preferred recreational activities throughout the study period.
A similar study was completed at the Addiction Research Foundation, the results of which have not been fully published, although Campbell (1976) has provided a brief account of its findings. In this study, young cannabis users were studied in a residential token economy in which they could earn tokens that could be exchanged for money and other goods by manufacturing woven woollen belts. Unlike the Mendelson study, subjects' cannabis doses were under the experimenters' control and subjects were given mandatory high doses. The subjects showed no gross behavioural changes, no social deterioration, and no alterations in intellectual functioning, but the results suggested, contrary to those of Mendleson et al, that chronic heavy cannabis use reduced productivity, especially during the period of mandatory high dosing (30mg of THC per day) which many subjects found aversive. It remains unclear how applicable the results of performance with mandatory high dosing are to the situation here users have control over their own dose.
The status of the amotivational syndrome remains contentious, in part because of differences in the appraisal of evidence from clinical observations and controlled studies. On the one hand, there are those who find the small number of cases of "amotivational syndrome" compelling clinical evidence of the marked deterioration in functioning that chronic heavy cannabis use can produce. On the other, there are those who are more impressed by the largely unsupportive findings of the small number of field and laboratory studies. Although the controlled studies have largely been interpreted as failing to substantiate the clinical observations (e.g. Millman and Sbriglio, 1986), the possibility has been kept alive by suggestive reports that regular cannabis users experience a loss of ambition and impaired school and occupational performance as adverse effects of their use (e.g. Hendin et al, 1987), and that some ex-cannabis users give impaired occupational performance as a reason for stopping (Jones, 1984). It seems reasonable to conclude that if there is an amotivational syndrome, it is a relatively rare consequence of prolonged heavy cannabis use. If this is the case, then studies of motivation and performance among dependent cannabis users may be the most promising place to look for examples of the syndrome.
Even if we assume that chronic heavy cannabis use impairs adult motivation and performance, there remains the question of mechanism (Baumrind, 1983). Is there a specific amotivational syndrome caused by the chronic intake of cannabinoids, or are we mistaking it for the impaired cognitive and psychomotor performance of chronically intoxicated dependent cannabis users (Edwards, 1976)? Are we perhaps mistaking a depressive syndrome among heavy cannabis users for the amotivational syndrome? (Cohen, 1982) Assuming that cases can be identified, how easy is it to reverse the syndrome or behaviour pattern after a period of abstinence from cannabis?
The evidence for an amotivational syndrome among adults is, at best, equivocal. The positive evidence largely consists of case histories, and observational reports. The small number of controlled field and laboratory studies have not found compelling evidence for such a syndrome, although their evidential value is limited by the small sample sizes and limited sociodemographic characteristics of the field studies, by the short periods of drug use, and the youthful good health and minimal demands made of the volunteers observed in the laboratory studies. It nonetheless is reasonable to conclude that if there is such a syndrome, it is a relatively rare occurrence, even among heavy, chronic cannabis users.