Cannabis Abuse and the Teenager’s Psychosocial Maturation


Cannabis Abuse and Cognitive Development during the Teenage Years

In post “Harmful Effects of Cannabis Smoking on Reasoning Ability, Memory and Sense of Coherence (Cognitive Functions)”, there is a discussion of the effects caused by long-term cannabis abuse on cognitive functions. From that discussion, it is clear that cannabis smoking has negative effects on a number of aspects, not least aspects which are of importance for more com plicated thought operations, planning, and the integration of impressions and previous memories, etc. It is worth repeating here that short-term memory is also called working memory, and that it is not just a “memory function” but a central location for the coordination of a number of mental functions which play an important role in enabling individuals to orient themselves relative to the surrounding world, such as planning, reorientation and reacting to new and unexpected circumstances. The scientific studies and clinical observations previously referred to concerned mainly adults; here we will look at what these kinds of cognitive disturbance can entail for teenagers, who are in a dynamic developmental phase.

In order to emphasise that teenagers are at least as sensitive as adults to the effects produced by cannabis on cognitive functions, I would like to refer to a study which was carried out on teenage subjects. Schwartz (), in a very thorough study, showed that long-term cannabis smoking at those relatively high THC concentrations (7 per cent) which were found already in the late 1980s in the United States led to a significant reduction in the short-term memory of the subjects. It is particularly noteworthy that some memory impairment remained six weeks after the first examination. Unfortunately, for financial reasons, the study did not continue beyond this point, but the findings are in line with the studies mentioned in Chapter “Harmful Effects of Cannabis Smoking on Reasoning Ability, Memory and Sense of Coherence (Cognitive Functions)” which showed that effects on cognitive functions persisted for a time after the abuse had ceased.

Identity Development, Formal Thinking and Cannabis Abuse

In this section, I deviate – for reasons which I hope will be obvious – from the structure found elsewhere in this report. By means of a slightly more extensive discussion, I try to place the study findings to which I refer in a larger context.

Baumrind and Moselle () maintain that many studies are not only deficient in terms of methodology, but also lack a theoretical foundation. With this type of research on complex relationships, it is necessary for studies to be based on an explicit theory of teenage development. This is necessary for the researchers to be able to draw up hypotheses, ask relevant questions and choose adequate study instruments. Without such a theoretical foundation, the risk is that studies will produce a bulk of disconnected statistical data which are difficult to deal with.

Having indicated some of the ways in which propitious youth development is made more difficult in the society of the 1980s, the authors go on to describe, stage by stage, the development which occurs during the teenage years. Baumrind and Moselle see a progressive transformation of “action schemas” from less integrated to more integrated systems as being the central thrust of youth development. They describe the manifestations of the maturation process within a range of different psychosocial categories. As in the psychoanalytically oriented development theories, the forging of a personal identity is a central element of this model. In this regard, this model resembles, in several ways, my own lines of thinking on the importance of social integration to the development of identity in the late teenage years (). In this context, we can also remind ourselves that several researchers from various disciplines have emphasised that the environment in which the teenagers of the Western industrialised societies of the 1980s and 1990s are to mature into adulthood seems to be hazardous in certain respects (). If this is so, drug abuse which makes this maturation process more difficult, or delays it, takes on an even greater importance.

Given our knowledge that cannabis produces negative effects on cognitive and other functions, it is of considerable interest to note that Baumrind and Moselle, like Steingart () and Ramström (), consider that certain stages of cognitive development – especially the ability for abstract thought – are crucial to the development of identity in the teenage years. According to Piaget, the child’s ability for concrete thinking is supplemented by the ability to perform formal thought operations at the age of 11–13 (though it has later been questioned whether this stage does not in fact normally occur somewhat later, at the age of 15–16). The ability to perform formal thought operations is the basis of the ability for abstract thought. At this stage, unlike during the period of concrete thinking, the young person is able to conceive of a world different from the actual reality before his or her eyes at any given moment. One new possibility that this development opens up for the young person is the ability to hold up his or her parents’ characters and mores to judgement, not rarely causing them pain.

But the ability for formal thinking also provides the foundation for long-term planning of the development of one’s own personality. Once an individual has reached this stage of cognitive development, he or she can move on from the kind of planning typical of the child (“When I grow up I’m going to be a millionaire”) to a kind of planning that reflects the increasing maturity of the adolescent (“By choosing a certain study programme at upper-secondary school and working to achieve certain grades, I can acquire the education I need for entry to the career that I want”). There is strong evidence that the functional shortcomings described in Chapter “Harmful Effects of Cannabis Smoking on Reasoning Ability, Memory and Sense of Coherence (Cognitive Functions)” as being characteristic of cannabis abusers are caused, in large part, by inadequate ability to perform formal thought operations ().

If the development of identity does not progress, the teenager remains at a childish level of development characterised by both a lack of independence and deficient integration in the adult world.

If we thus place our knowledge of the mechanisms by which cannabis produces its effects, mainly as regards its impact on cognitive functions, in relation to a central and crucial element of the mental development of the teenager (the forging of identity), we can see how prolonged smoking of hashish during the teenage years may result in the stagnation of psychosocial development. Still, even though the interaction just described affects the core of teenage development – the forging of identity – and is therefore very important, we must not forget that the impairment of mental functions can have a range of other effects. Deterioration of short-term memory obviously makes learning more difficult, but it also has a negative effect on the individual’s ability to make plans, to establish new relationships and to make realistic assessments of the world around him or her.

In recent years, researchers have also found that the consumption of cannabis in the early teenage years has a causal connection with mental and social disturbances in the later teenage years and early adulthood. Quite a few of these disturbances have been mentioned already: psychosis (), depression and suicidal thoughts (), and criminality and unemployment ().


Selections from the book: “Adverse Health Consequences of Cannabis Use. A Survey of Scientific Studies Published up to and including the Autumn of 2003