Elizabeth C. Temple

The 'grass ceiling': limitations in the literature hinder our understanding of cannabis use and its consequences.

AIM To illustrate how limitations in the cannabis literature undermine our ability to understand cannabis-related harms and problems experienced by users and identify users at increased risk of experiencing adverse outcomes of use. METHOD AND RESULTS Limitations have been organized into three overarching themes. The first relates to the classification systems employed by researchers to categorize cannabis users, their cannabis use and the assumptions on which these systems are based. The second theme encompasses methodological and reporting issues, including differences between studies, inadequate statistical control of potential confounders, the under-reporting of effect sizes and the lack of consideration of clinical significance. The final theme covers differing approaches to studying cannabis use, including recruitment methods. Limitations related to the nature of the data collected by researchers are discussed throughout, with a focus on how they affect our understanding of cannabis use and users. CONCLUSIONS These limitations must be addressed to facilitate the development of effective and appropriately targeted evidence-based public health campaigns, treatment programmes and preventative, early intervention and harm minimization strategies, and to inform cannabis-related policy and legislation.

Taste development: differential growth rates of tongue regions in humans

There is a paucity of information about the anatomical and functional development of the human gustatory system. Although the anatomical development of the taste-sensitive fungiform, circumvallate and foliate papillae in the respective anterior, posterior and latero-posterior regions of the dorsal surface of the tongue has been well documented in the fetus, there is limited information about how these regions grow and when they exhibit adult function. The present study is concerned with determining when the growth of one of these taste-sensitive regions becomes adult in size, namely, the anterior region, and how this growth compares with that of the remaining posterior region. Two-hundred and thirty-two living subjects aged between 4 and 32 years participated. Following the identification and marking of a series of landmarks on the dorsal surface of the tongue with blue food dye, five measurements of the width and length of various parts of the tongue allowed calculation of the growth of the anterior and posterior regions. The results indicate that the fungiform papillae-rich anterior region attains adult-size by 8-10 years of age whilst the posterior region continues to grow until 15-16 years. Interestingly, this early development is not matched by achievement of adult function [Dev. Brain Res. 82 (1994) 286] or adult size papillae or taste pores [Dev. Brain Res., submitted]. Finally, the findings of the present study will allow studies of the development of taste function in humans to be conducted using equivalent tongue areas in subjects of different ages.

A Theoretical Approach to Resolving the Psychometric Problems Associated With the Zimbardo Time Perspective Inventory

The Zimbardo Time Perspective Inventory (ZTPI; Zimbardo & Boyd, 1999) assesses five time-related constructs – Past Negative (PN), Past Positive (PP), Present Fatalistic (PF), Present Hedonistic (PF), and Future (F) – and is one of the most frequently used time measures in the extant literature. Versions of the ZTPI have been translated into a variety of languages, but the psychometric support for ZTPI scores remains contested. We examined the internal consistency, structural validity, and convergent validity of scores on a version of the ZTPI that consisted only of items that specifically referenced time constructs, the ZTPI-TP. Participants consisted of five samples of adolescents and adults from four countries: Australia (653 adults), Slovenia (425 adolescents and adults), the United Kingdom (913 adolescents; 455 adults), and the United States (815 adolescents). Structural validity analyses provided stronger support for ZTPI-TP scores than for ZTPI scores, and convergent validity evidence also provided support for ZTPI-TP scores. However, analyses revealed that the PF and PH factors were still problematic, especially with regard to factor coefficients and internal consistency estimates. We concluded that the ZTPI-TP can form the basis for a more robust version of the ZTPI.

The association between cannabis use, mental illness, and suicidal behavior: what is the role of hopelessness?

Cannabis is one of the most common illegal psychoactive substance used in European countries, in particular among adolescents and young adults (1). It has been estimated that almost 55% of adolescents aged 15–19 years have used cannabis at least once in their lifetime (2), while past year use is reported by approximately 30% of 15–17 year olds and over 47% of those aged 18–19 years (3). Cannabis use has been associated with several adverse life outcomes including unemployment, legal problems, dependence, early school leaving, increased risk of developing both psychotic and affective disorders (3, 4) together with brain structural and functional abnormalities (5, 6). An association between cannabis use, psychiatric disorders and suicidal behavior has also frequently been reported, although the exact nature of this link is still poorly understood (4). Globally, suicide is one of the most common causes of death among young people aged 10–24 years (6% of deaths), exceeded only by motor vehicle accidents (10%) (7). Over the last decade suicidal behavior has increased among adolescents and young adults, there has also been a trend toward the earlier initiation of cannabis use (8). This has led researchers to investigate the associations between the two factors to determine if cannabis use may be considered a factor that can trigger suicidal behavior. Evidence indicates that cannabis use is significantly associated with both attempted and completed suicides among healthy youths (9) and both twin studies (10) and case-control comparisons (11) have shown the increased risk of suicide ideation/attempts in those who use cannabis. Moreover, a longitudinal study found that frequent cannabis use (at least several times a week) predicted later suicidal ideation in susceptible males but not females (12). The earlier that this intense use first occurred and the higher the frequency of cannabis use, faster the susceptible individuals experienced suicidal thoughts. Frequent and early cannabis use has also been associated with impaired mental wellbeing among young individuals (13, 14), and the risk of developing psychiatric conditions such as psychosis (15) and major affective disorders (16). Specifically, evidence suggests that cannabis use may exacerbate pre-existing conditions such as bipolar disorder, and predict negative outcomes and psychosocial impairment (17, 18). According to longitudinal studies, the high and frequent use of cannabis is also associated with longer recovery times for affective conditions, more hospitalizations, poorer compliance with treatment, increased aggression, and poorer response to treatment in patients with bipolar disorder type I and II (12, 17). Nevertheless, it is important to note that many of the studies investigating associations between cannabis use and psychiatric conditions are cross-sectional in nature and cannot establish a causal relationship between the two phenomena (19). Further, several studies (20, 21) suggest a bidirectional relationship, as cannabis use variables do not solely explain the psychiatric outcomes observed nor do pre-existing psychiatric conditions fully explain the increased use of cannabis. Some researchers (22) have suggested that individuals with high levels of anxiety sensitivity or hopelessness may be more sensitive to the negative reinforcement processes of substance use (i.e., the ability of substances to modulate negative affective states) than non-affected individuals; however, some individuals experiencing the onset of mania or depression are not more likely to report increased cannabis use than those not experiencing these disorders (23, 24). In addition, other authors (25) have questioned the hypothesis that individuals may use cannabis to self-medicate psychotic or depressive symptoms. In summary, cannabis use may be considered only as a risk factor, and possibly one of a great many that may predict the onset or exacerbation of affective disorders and suicidal behavior (26). Thus, whether cannabis use can trigger psychiatric disorders or only precipitate or exacerbate psychiatric conditions in vulnerable individuals, is still poorly understood.

Cannabis use and anxiety: is stress the missing piece of the puzzle?

Objective: Comorbidity between anxiety and cannabis use is common yet the nature of the association between these conditions is not clear. Four theories were assessed, and a fifth hypothesis tested to determine if the misattribution of stress symptomology plays a role in the association between state-anxiety and cannabis. Methods: Three-hundred-sixteen participants ranging in age from 18 to 71 years completed a short online questionnaire asking about their history of cannabis use and symptoms of stress and anxiety. Results: Past and current cannabis users reported higher incidence of lifetime anxiety than participants who had never used cannabis; however, these groups did not differ in state-anxiety, stress, or age of onset of anxiety. State-anxiety and stress were not associated with frequency of cannabis use, but reported use to self-medicate for anxiety was positively associated with all three. Path analyses indicated two different associations between anxiety and cannabis use, pre-existing and high state-anxiety was associated with (i) higher average levels of intoxication and, in turn, acute anxiety responses to cannabis use; (ii) frequency of cannabis use via the mediating effects of stress and self-medication. Conclusion: None of the theories was fully supported by the findings. However, as cannabis users reporting self-medication for anxiety were found to be self-medicating stress symptomology, there was some support for the stress-misattribution hypothesis. With reported self-medication for anxiety being the strongest predictor of frequency of use, it is suggested that researchers, clinicians, and cannabis users pay greater attention to the overlap between stress and anxiety symptomology and the possible misinterpretation of these related but distinct conditions.

The Zimbardo time perspective inventory: Time for a new strategy, not more new shortened versions

Researchers continue to attempt to resolve the psychometric problems associated with the five-factor Zimbardo Time Perspective Inventory through the development of shortened forms of the scale. These atheoretical efforts have been data driven and have resulted in scales whose reliability and validity have not been subsequently supported. The purpose of this paper was to explore the factorial validity and reliability of new short scales on samples independent from which they were developed. We used data from five different samples in four different countries (Australia, Britain, Slovenia, and the United States) to examine the psychometric validity and reliability of three recently developed scales, the ZTPI-20, ZTPI-17, and ZTPI-15. Results regarding validity were equivocal for all scales and reliability coefficients were suboptimal in all samples. We conclude by stressing the necessity for a theoretically driven approach to enhancing the psychometric assessment of time perspective rather than simply sacrificing reliability or discriminant validity for improved model fit in a shorter scale.

Clearing the smokescreen: the current evidence on cannabis use.

Decisions regarding the legal status of cannabis have long been framed (for the public at least) with reference to the perceived health risks and harms associated with use. Yet, drug policy and legislation relating to the use of cannabis are rarely based on the scientific evidence of the known risks and harms. There are many reasons for this discrepancy, with the politicization of cannabis use, where ideology and moralizing are given precedence over the science, being one. Thus, we begin this research topic with Aggarwal (1) discussion of how such politicization has contributed to the current smokescreen that is obscuring our understanding of cannabis, including the impact it has on the ability of researchers to collect and disseminate accurate information about the effects of cannabis use. The capacity of policy makers and legislators to develop evidence-based cannabis policies and laws is also contingent on researchers explaining the existing evidence, disseminating new research findings, and collaborating with relevant people, agencies, and government departments to improve the premises on which they base their policies and legislation. Roffman (2), who took this path through his involvement in the development of the legislation to legalize cannabis use in Washington State, provides an insider’s view of the processes and deliberations. While we will have to wait for the evaluation of this carefully designed model for regulating cannabis use, the following two articles provide some insight into patterns of cannabis use in contexts were consumption is relatively normalized. There are many parallels evident in the findings of Mostaghim and Hathaway (3) qualitative exploration of cannabis use among Canadian university students and Liebregts et al. (4) prospective investigation of cannabis use by young adults transitioning from university to work in The Netherlands. Of particular note are the ways in which the participants’ self-identity, including priorities, roles, and responsibilities, act as constraints to their use, and the clear demarcations drawn between leisure and work. A major consideration, discussed by Roffman (2), was the risk that legalization of cannabis might spark an increase in usage, which could, in turn, result in higher incidence and prevalence of cannabis-related harms, particularly if there was an increase in use by adolescents. The evidence underpinning concerns of adverse impacts resulting from early onset cannabis use is reviewed by Chadwick et al. (5), who report that adolescent users with genetic vulnerabilities are at increased risk of experiencing motivational, affective, and psychotic disorders, including schizophrenia. The association between cannabis and psychosis/schizophrenia is comprehensively reviewed by Radhakrishnan et al. (6), who conclude that, while, cannabis may be a component cause in the development of psychosis, this association is moderated by family history of psychoses, genetic factors, childhood trauma/abuse, and age at onset of use. The importance of differentiating between psychotic disorders and psychomimetic effects is also highlighted as being an essential step in increasing our understanding of the cannabis-psychosis association. Similarly, the two pathways from cannabis use to psychosis proposed by Burns (7) illustrate the importance of differentiating between types of cannabis-psychosis trajectories, showing how the clinical presentation profiles and treatment outcomes differ for early onset, long-term cannabis use in comparison to later onset, short-term but intense use. Early onset/adolescent cannabis use is investigated further in the next three articles. First, Serafini et al. (8) explore the possible role of hopelessness as a mediator in the relationship between early cannabis use and suicidal behaviors, while Little et al. (9) investigate predictors of cannabis cessation within a sample of high-school students. The next article, by Fallu et al. (10), reports the findings of a latent class analysis of adolescent cannabis users, revealing four different use trajectories. The early onset, heavy cannabis and polydrug use group in this study were found to experience the highest level of use-related problems, followed by the late-heavy-polydrug group. Similarly, Connor et al. (11) report that, in a sample of adult cannabis users referred for treatment, those who engaged in polydrug use were more likely to be cannabis dependent and experiencing higher levels of comorbid psychopathology, than individuals who used cannabis, tobacco, and/or alcohol. Healey et al. (12) also focused on a treatment sample, finding that both cannabis users and their clinicians reported difficulty in establishing a therapeutic bond. A dose–response relationship was evident for the client perspective, such that heavier users reported feeling less connected, which the authors suggest may be related to effects of cannabis use such as paranoia or anxiety. The association between cannabis use and anxiety is explored by Temple et al. (13), who test the premise that the contradictory findings in the literature for this association may be due to individuals misattributing stress responses to anxiety symptomology. The finding that stated use to self-medicate for anxiety is more strongly associated with level of stress rather than anxiety symptoms provides some support for this hypothesis. The therapeutic potential of cannabis is one of the factors driving the push for legalization of cannabis use. Yet, as discussed by Crippa et al. (14), with the majority of past research focus being on cannabis as a whole or THC, we have limited knowledge of the mechanisms of action of the many other cannabinoids, which is impeding our understanding of their medical applications. One of the key areas of current research into the therapeutic effects of cannabis focuses on the ability of CBD to modulate the adverse psychological effects of THC; this body of evidence is reviewed here by Niesink and van Laar (15). Oliere et al. (16) similarly focus on the therapeutic potential of cannabinoids, comprehensively reviewing what is known about the role of the endocannabinoid system in addiction and demonstrating the possibility of using cannabinoids to treat stimulant dependence. The focus on individual cannabinoids is also relevant to the issue of doping in sports, as is discussed by Bergamaschi and Crippa (17), who point out that focusing on THC metabolites for drug testing ignores the performance enhancing potential of other cannabinoids, such as CBD and CBN. The final article in this research topic, by Burns et al. (18), urges researchers to reflect on the different indicators of cannabis use, demonstrating how the data we collect and inferences drawn will differ if we focus on the prevalence of cannabis use, for example, rather than the quantity of cannabis used or the frequency of use. This article, along with the others collected here, encourage cannabis researchers to reflect on the ways in which we frame our research questions, design our studies, and explain our findings, so as to improve the clarity of the evidence. While we may not be able to clear the politicized smokescreen currently shrouding the evidence, ultimately, it is our responsibility to ensure that there is a comprehensive body of scientific knowledge available for the development of evidence-based cannabis policies and legislation when the fresh air does eventually blow through.

Commentary on van der Pol et al. (2014): Reconsidering the association between cannabis exposure and dependence

The existence of a positive, and relatively strong, association between cannabis exposure/tetrahydrocannabinol (THC) dose and cannabis dependence is an assumption on which much cannabis-related research, public policy and health advice has been based. Van der Pol et al.’s [1] findings, however, throw this into some doubt. To understand why there is a discrepancy here, and its import, it is essential to consider how cannabis exposure/dose is typically measured and, thereby, how past studies may have clouded our understanding of the association between cannabis use and dependence. Cannabis exposure has been assessed in a variety of ways, tending to include measurement of some combination of age at first use, duration of use, quantity consumed and frequency of use, with the latter often employed in isolation as a proxy for THC dose [2]. Although known to be only approximations of exposure, these variables are used by researchers for a number of reasons. Foremost among these are the efficiencies associated with the use of self-report questionnaires, which are often completed anonymously by participants and remotely from researchers. The classification of cannabis as an illicit substance within most jurisdictions globally, however, also acts to prevent the vast majority of cannabis researchers from undertaking as thorough an assessment of cannabis exposure/dose as has been demonstrated by van der Pol et al. [1]. In the relatively small number of studies where THC dose has been confirmed, this has generally been via ‘cannabis cigarettes’ purchased from the US National Institute on Drug Abuse (NIDA). These studies, however, do not replicate normal usage of cannabis, such as that assessed in van der Pol et al.’s study. Specifically, NIDA joints range from 3 to 7% in THC content and are typically smoked in a prescribed manner (i.e. uniform puff size/duration and breath hold) (e.g. [3]); in comparison, van der Pol et al.’s participants were using cannabis ranging from 3.6 to 15.7% THC and they smoked it as per usual, such that their smoking topographies varied. Taken together with the finding that total number of puffs and puff volume were significant predictors of dependence in van der Pol et al.’s study, these differences throw at least some doubt on the ‘real world’ validity of findings from previous studies (whether using real or proxy measures of exposure/dose) and illustrate how important naturalistic studies are to increasing our understanding of the acute and long-term effects of cannabis use, including dependence. Of particular interest here is the ‘typical’ smoking topography that van der Pol et al. [1] found was predictive of cannabis dependence. Taking more frequent puffs of greater volume when commencing a session is evocative of someone seeking a quick hit, such as to ‘take the edge off’, then smoking with less urgency as the desired effects kick in. As such, the ‘typical’ smoking topography may be indicative of using cannabis to cope with psychological distress/stress. Such an interpretation would be in line with findings from two other studies from the same research team, which also found that cannabis exposure/ THC variables did not distinguish dependent from nondependent users [4] nor predict future dependence in frequent users [5]. Instead, these studies found that cannabis dependence was predicted by consuming cannabis alone, use for coping and expansion motives, use of other substances and comorbid mood and anxiety disorders [4], and living alone, coping motives for use and stress [5]. These findings are supportive of the self-medication hypothesis [6], and consistent with both Van Dam, Bedi & Earleywine’s [7] proposition that anxiety is causally related to the development of abuse/dependence in heavy users, and Buckner & Carroll’s [8] finding that, within a cannabis-dependent sample, reducing anxiety led to reduced cannabis use yet reducing cannabis use did not lead to decreased anxiety. Evidently, research is needed to further this line of inquiry and, particularly, to test the posited link between ‘typical’ smoking topographies, psychosocial distress/ stress and coping motives for use. While most cannabis researchers will not be able to complete as extensive an assessment of cannabis exposure/THC dose as van der Pol et al. [1], it should be possible to include additional items within self-report questionnaires or interview schedules; for example, to determine what proportion of a joint participants typically consume to achieve their desired state and whether their smoking topography is ‘typical’ or ‘atypical’ in nature. Furthermore, we need to question our assumptions about the association between cannabis exposure/THC dose and dependence, including being open to the possibility that our understanding of cannabis dependence may be more accurate if dependence is viewed as being indicative of a user who is experiencing comorbid psychosocial distress/stress. This is not to ignore the possibility that cannabis use by such individuals may also act to exacerbate their condition, but rather to recognize that cannabis exposure/THC dose itself may be less important to our understanding or COMMENTARY bs_bs_banner