This study builds upon a small previous literature documenting the prevalence and frequency of various adverse reactions to cannabis. Specifically, Sexton et al. (2019) recently asked a large sample (> 2900) of cannabis users to indicate which of a list of acute effects (positive and adverse) they experience when they are intoxicated on cannabis. Their results indicated that dry mouth was the most prevalent adverse reaction to cannabis (63% of their sample endorsed experiencing this reaction), followed by memory problems (42.2%), tiredness (45.9%), and altered sense of time (37.6%). Further, they found that paranoia (14.5%), anxiety (8.6%), lung discomfort (7.6%), dizziness (5%) and hallucinations (3.8%), were less commonly endorsed adverse reactions. In contrast, findings from the present study indicate that paranoia (50.3%), anxiety (53.2%), coughing fits (62.2%), chest/lung discomfort (30.7%), dizziness (39.3%), and hallucinations (17%) are experienced by a larger percentage of cannabis users, with anxiety, paranoia, and dizziness reported on approximately 25% of cannabis use sessions, coughing fits reported on approximately 40% of all sessions, chest/lung discomfort reported on approximately 30% of cannabis use sessions, and auditory hallucinations experienced on approximately 20% of these sessions. The discrepancies in these findings may reflect differences in the methods of assessing these reactions and/or the samples surveyed. Specifically, Sexton et al. (2019) simply asked respondents to indicate which reactions they experience while intoxicated while we asked respondents to indicate which reactions they had ever experienced while intoxicated. As such, participants in Sexton’s (2019) study may have reported on which they more commonly experience rather than which they had ever experienced. Further, the participants in Sexton’s study were a broader community sample of recreational, medical, and mixed (recreational and medical) users with a wider range of ages than participants in the present study (which focused predominantly on young recreational users). It is possible that older, more experienced cannabis users experience fewer adverse reactions. Indeed, their findings did indicate that older users and medical users were less likely to report adverse reactions than younger recreational users (Sexton et al. 2019). Collectively these findings suggest that younger, less experienced, recreational cannabis users may be more prone to experiencing adverse reactions to cannabis.

Arendt et al. (2007) measured the frequency of various reactions (positive and negative) to acute intoxication in a relatively small sample of 119 cannabis-dependent individuals. Their results indicated that altered perceptions, delusions, slower movements, and confusion were the most frequent adverse reactions to cannabis intoxication (with mean ratings between sometimes and often). In contrast, hallucinations, self-reported feelings of anxiety, and sadness/depression during intoxication were infrequent in their sample (with mean ratings indicating these reactions are rarely experienced). The present study focused on largely different reactions than theirs and results from our study indicate that anxiety and hallucinations are experienced more frequently (on approximately 20–25% of all cannabis use sessions). Once again, it is likely that differences in the samples used in these studies accounts for differences in our findings. The cannabis-dependent individuals in Arendt et al.’ (2007) study likely have more experience with cannabis and as such may be more tolerant to its potentially adverse effects.

This study extends upon previous research that has focused exclusively on prevalence (Sexton et al. 2019) and frequency (Arendt et al. 2007) of adverse reactions by further indicating which reactions are perceived as the most and least distressing by cannabis users. It is worth noting that overall, even the most distressing reactions to cannabis were only rated between ‘moderately’ and ‘quite distressing,’ on average, suggesting that cannabis users do not, in general, find acute adverse reactions to cannabis to be severely distressing. Further, feelings of body humming, numbness, and unsteadiness were rated as the least distressing, with participants on average indicating that these specific reactions were between ‘not at all’ to ‘slightly’ distressing. As such, these reactions to cannabis intoxication may not actually be interpreted as adverse by cannabis users and could be removed from the ARS for future studies. In contrast, paranoia and anxiety were rated as ‘moderately distressing’ on average and were also highly prevalent and frequent. Consequently, these potential adverse reactions may be of more concern, and should be emphasized as the most common distressing reactions.

The results of the standard regression analysis using all 22 predictors to predict the frequency of adverse reactions to cannabis revealed that only frequency of cannabis use accounted for a significant portion of unique variance in this outcome. The regression coefficient was moderately sized and negative, indicating that more frequent cannabis use is associated with less frequent adverse reactions to cannabis. This indicates that regular cannabis users, who are more accustomed to the acute effects of cannabis, experience adverse reactions during a smaller percentage of their cannabis use sessions. This may be due in part to the development of tolerance to the intoxicating effects of cannabis, which occurs with regular cannabis use. Indeed, past research has also found that regular cannabis users can develop tolerance to the cognitively impairing effects of cannabis (Colizzi and Bhattacharyya 2018; D’Souza et al. 2008; Ramaekers et al. 2016), and partial tolerance to the anxiogenic, psychotomimetic, and cardiac effects of cannabis also occurs with regular exposure (Colizzi and Bhattacharyya 2018). Additionally, experienced cannabis users are likely better accustomed to self-titrating their cannabis ingestion when they have reached their desired level of intoxication, whereas less frequent users may not properly self-titrate. Alternatively, our results may indicate that individuals who frequently experience adverse reactions may find cannabis less desirable and choose to use the drug less often.

Symptoms of cannabis use disorder, conformity motives, and anxiety sensitivity, each accounted for significant portions of unique variance in the number of different adverse reactions to cannabis experienced, as well as in the levels of distress produced by these reactions. Each of these regression coefficients was small and positive, indicating that problematic cannabis use, cannabis use motivated by a desire to fit in with peers, and higher levels of anxiety sensitivity are associated with reporting a greater number of different adverse reactions, and with experiencing higher levels of distress during these reactions.

By definition, individuals with more severe symptoms of cannabis use disorder continue to use cannabis despite experiencing negative consequences associated with their use (e.g. problems with memory, impairment in functioning; Adamson et al. 2010). Our results appear to indicate that individuals with more severe symptoms of cannabis use disorder also might continue to use cannabis despite experiencing numerous distressing acute adverse reactions to cannabis, whereas individuals with lower levels of these symptoms may be more likely to cease cannabis use after experiencing a variety of distressing adverse reactions to cannabis.

Individuals using cannabis to conform to peer pressure may be less experienced users who are not accustomed to, nor enjoy, the acute effects of cannabis intoxication, but use cannabis to fit in with their peers. This seems to suggest that one’s expectations for the effects of cannabis and/or their mindset prior to cannabis use may shape the valence of their experience while intoxicated and that those using specifically for conformity motives are more likely to experience a variety of acute, distressing reactions to cannabis.

Individuals with higher levels of anxiety sensitivity also reported a greater variety of adverse reactions, and experienced higher levels of distress associated with these adverse reactions. Anxiety sensitivity refers to the tendency to fear anxiety-related sensations and to catastrophize about the meaning of these sensations. Acute cannabis intoxication can cause elevated heart rate, anxiety, paranoia, and other anxiety-like symptoms. It is therefore unsurprising that individuals higher in this trait are more likely to notice, report, and feel distressed by these reactions.

Lastly, agreeableness was found to predict a significant portion of unique variance in the total number of different reactions endorsed, and conscientiousness predicted a significant portion of unique variance in distress associated with adverse reactions to cannabis. Each of these regression coefficients was small and positive, indicating that higher levels of these personality traits were associated with increased levels of these aspects of adverse reactions to cannabis. More specifically, the results indicate that individuals who are more agreeable are more likely to endorse a wider variety of adverse reactions. It is unclear whether this is a response bias (i.e., whether these individuals are simply more likely to agree that they have experienced these reactions). Bivariate correlations between agreeableness and the number of different reactions experienced and between conscientiousness and the distress levels associated with adverse reactions revealed that these personality traits were not significantly correlated with these aspects of adverse reactions to cannabis. This pattern of results suggests that these two personality variables are acting as suppressor variables (i.e., suppressing error variance in other predictors, making them stronger predictors of these outcome variables). As such, these results may be largely spurious and additional research is needed to confirm the validity of these unexpected results.

Limitations to this study primarily relate to the reliance on cross-sectional survey data from a self-selected university student sample primarily comprising white (> 70%) female (> 70%) recreational (> 90%) cannabis users who, on average, used cannabis at a moderate frequency. Therefore, while a university student sample was intentionally sought because this population is known to use cannabis at high rates (SAMHSA 2016), the present results may not generalize to other populations of cannabis users. As such, future research should seek to replicate these findings in more diverse samples. Additionally, while our sample of cannabis users reported using a variety of cannabis use methods, consistent with previous research (Sexton et al. 2016), the majority of the sample (> 80%) reported predominantly using inhalation methods of administration, while less than 15% reported predominantly using an oral route of administration. As such, the present results may not reflect adverse reactions associated with oral or other routes of administration as well as they reflect more traditional inhalation methods. Further, these reactions were retrospectively assessed and therefore may be prone to recall bias. An additional limitation to this study pertains to the fact that the adverse reactions documented in this study were predominantly physiological and psychological. Future research should expand upon these reactions to include a wider range of possible social, emotional, and physical reactions to cannabis intoxication (e.g., dry eyes). Finally, the DASS-21 was used to assess the relationships between negative affect variables (depression, anxiety, and stress) and ARS outcomes. However, the DASS-21 assesses mood over the past week, while the timeframe covered by the ARS is indefinite. As such, it is possible that this study failed to detect relationships between negative affect variables measured by the DASS-21, and ARS outcomes because of the differences in time frame assessed by these two measures.