People’s levels of cognitive and emotional functioning—and thus, their ability and motivation to successfully self-regulate—have been shown to fluctuate over the course of the waking day, often declining later at night (Schmidt, Collette, Cajochen, & Peigneux, 2007). Indeed, impairments in some cognitive functions emerge after being awake for only 14 hours (e.g., monitoring and awareness; Zhou et al., 2012), which roughly equates to 9pm if the individual has been awake since 7am. On average, most people tend to experience decreasing alertness from approximately 6pm onwards (Åkerstedt, Folkard, & Portin, 2004) and increasing tiredness after 12 hours of being awake (Sagaspe et al., 2006). Further, being awake for 17 hours (i.e., midnight, if awake since 7am) causes lowered performance in psychomotor vigilance equivalent to that of 2–3 standard drinks (Dawson & Reid, 1997). Moreover, these dips or troughs in capacities required for self-regulation are expected to occur even sooner at night for those with a morning chronotype or “early birds,” compared to evening types or “night owls” (Kerkhof, 1998)—and also for people with a cumulative sleep debt from consecutive nights of insufficient sleep (Dinges et al., 1997; Roehrs et al., 2003). Each of these findings from the sleep science literature is concerning given what we know from the substance use literature about when people tend to most often drink alcohol and/or use club/party drugs: at night-time, and especially Friday and Saturday nights (see Shiffman, 2009 for review). However, these two literatures are not often considered together.

There is also evidence suggesting that self-regulation in other behaviors is more difficult at night—for example, people attempting to quit smoking or to adhere to dieting most commonly lapse at night (Fillo et al., 2016; Forman et al., 2017; McKee, Ntoumanis, & Taylor, 2014). Sleep deprivation has also been linked with increased risk-taking (see Womack, Hook, Reyna, & Ramos, 2013, for a review), the increased tendency to select the easier, less demanding task in complex situations (Engle-Friedman et al., 2003), and greater delay-discounting (Reynolds & Schiffbauer, 2004). That both tiredness and substance use are likely to occur at night is further compounded by the finding that cravings for alcohol occur most often at night (Piasecki et al., 2011). Each of these findings has implications for the tired individual when choosing between an easy, immediate pleasure (say, the fourth drink with friends) and a more complex, delayed alternative (say, postponing gratification and defending one’s choice of water). That the time for making substance use decisions frequently coincides with the time-of-day when individuals are tired or “not in their circadian prime” for exercising self-regulation (depicted in Figure 1), is described by “circadian misalignment” which refers to the mismatch between an individual’s internal circadian preference and the external demands of social schedules or daily life (Baron & Reid, 2014; Curtis, Burkley, & Burkley, 2014; Wittmann et al., 2006). Yet tiredness and circadian misalignment are rarely counted among the factors that amplify risk in substance use.

Although there are numerous studies on the detrimental effects of alcohol and drugs on sleep quality (see Angarita et al., 2016; Brower, Aldrich, & Hall, 1998, for reviews) and on links between sleep disturbance and relapse outcomes (Brooks et al., 2016), research has yet to adequately explore the possibility of a bidirectional relationship between tiredness and drinking (Roehrs & Roth, 2001; Hasler, Smith, Cousins, & Bootzin, 2012). One exception is a recent daily diary study which showed that shorter sleep on a given night predicts greater alcohol use the following day (Fucito et al., 2017). Another study tested a model linking sleep problems to substance use through impaired emotion regulation in adolescents (Edwards, Reeves, & Fishbein, 2015). More generally, sleep health has also gained recognition in recent models of health behavior (Barber, 2014; Hagger, 2014). Relatedly, chronotype research has observed that evening types report greater rates of substance use (e.g., Adan, 1994; Hasler, Soehner, & Clark, 2014; Urbán, Magyaródi, & Rigó, 2011), and this may be partly because, compared to morning types, evening types have more energy for effortful behaviors at night and greater exposure to opportunities for use. However, this overlooks the fact that many morning types may still be making their substance use decisions at night, when they may be tired.

A number of studies have looked at tiredness as a risk factor in adults’ alcohol use, generally finding that those with poorer sleep quality or shorter sleep length report greater substance use (e.g., Chaput et al., 2012) or stronger motives of drinking to cope (Digdon & Landry, 2013). Further, a recent study found that daily sleep quality influences craving for alcohol and drugs via its impact on reduced positive affect (Lydon-Staley et al., 2016). Another study of heavy-drinking college students tested a model in which poorer sleep quality partially mediated the association between poor mental health and drinking (Kenney et al., 2013). Furthermore, two recent studies have observed links between poor sleep quality and drug use among gay and bisexual men (GBM; Downing et al., 2016; Duncan et al., 2016). However, more research on tiredness and substance use is needed—especially among GBM who, as a group, face disparities in substance use (Kerridge et al., 2017) and in adverse outcomes of sexual risk-taking which has been linked with use (Feinstein & Newcomb, 2017), namely HIV (CDC, 2016). Emerging evidence also suggests that GBM and other sexual and gender minority groups tend to experience poorer sleep relative to heterosexuals (e.g., Chen & Shiu, 2017; Galinsky et al., 2018; Patterson, Tate, Sumontha, & Xu, 2018), and thus the study of the effects of tiredness on health behaviors among this population appears especially relevant.

Accordingly, we contend that time of day and tiredness are important factors to consider in substance use behavior for two reasons: (1) that many people may be making substance use decisions later than their optimal time of cognitive and emotional functioning, implicating circadian misalignment, such that their tiredness may situationally impair their capacity to self-regulate (Millar, 2017); and (2), that tiredness itself may motivate individuals to use substances to lift their falling energy levels.

The use of alcohol mixed with energy drinks (Grandner et al., 2014) or of stimulant drugs in the battle against feeling tired makes intuitive sense, and is especially common among gay and bisexual men (Wells et al., 2013). However, there is also evidence that alcohol alone (without energy drinks) may also temporarily lift energy due to its more immediate stimulatory effects, which are perhaps less acknowledged than its more delayed sedative effects (Hendler et al., 2013). Indeed, these two kinds of effects of alcohol are described by the Biphasic Alcohol Effects Scale (Martin et al., 1993), which assesses seven subjective states associated with alcohol’s stimulatory effects (e.g., feeling energized, excited, up) and seven associated with its sedative effects (e.g., feeling down, heavy-headed, sluggish). That these stimulatory effects of alcohol may motivate the tired individual is reflected in colloquial terms such as wanting a “pick-me-up” or a “livener.” Although enhancement motives were counted among drinking motives (Cooper, Russell, Skinner, & Windle, 1992), research has yet to adequately consider whether tiredness motivates alcohol use, independent of energy drinks.

In sum, time of substance use, concomitant tiredness, the role of circadian misalignment, and tiredness as a motivator of substance use are underappreciated factors in substance use behavior. Accordingly, we aimed to gather preliminary data on these factors by drawing on two different datasets, both in relation to GBM in the U.S.—although it is anticipated that similar dynamics may be at work in other populations. We hypothesized that the majority of GBM would report nighttime (here, 9pm or later) as the time when they most frequently use substances [Hypothesis 1]. We also hypothesized that, although reporting this later time for substance use would be more common among those with a later chronotype, there would be a substantial proportion of morning types who report this later time for most frequent use, potentially implicating circadian misalignment [Hypothesis 2]. Finally, we hypothesized that a substantial proportion of men would endorse the motivation of using substances to help stay awake when tired [Hypothesis 3]. No hypotheses were advanced for whether endorsement of this motivation would vary by chronotype, as both morning and evening types may use substances to stay awake but at different times of night. We also aimed to consider age in these associations because younger age is associated with greater eveningness preference (Randler, 2016; Roenneberg et al., 2007), later times for drinking (Dawson, 1996), and less sensitivity to the sedative effects of alcohol (Spear, 2000). Given the exploratory nature of these analyses, we also tested for potentially relevant demographic differences in these distributions.

As displayed in Table 1, the sample of 2,814 alcohol-using men utilized for Hypotheses 1 and 2 in relation to alcohol had a mean age of 37.7 (SD = 13.3), was mostly White (62.8%), HIV-negative (83.5%), gay (82.3%), and single (62.4%). On average, evening types (56.8%) were younger (M = 35.4, SD = 12.3) than morning types (M = 42.5, SD = 13.9; 28.2%) and intermediate types (M = 37.4, SD = 13.7; 15.0%), F(2, 2811) = 79.27, p < 0.001.

The majority (51.3%) of these 2,814 alcohol-using men reported that their time of most frequent drinking was from 9pm onwards, followed by evening or 5–9pm (46.2%). Only 2.5% reported drinking most often during the day. Bivariate comparisons showed that intermediate types (50.9%) and evening types (60.4%) were more likely than morning types to report this later time for most frequent drinking (9pm onwards). However, almost one-third (33.2%) of morning types did report this 9pm-or-later time. Further, bivariate comparisons showed that reporting this 9pm-or-later time was more common among younger men, men of color, single men, those with less education, and those who were recruited from the hookup app or Facebook. Table 2 displays the multivariable results, where each of these differences remained significant except for education.

Of the 449 men who reported recent club/party drug use, the majority (75.1%) reported most frequent use occurring from 9pm onwards, followed by evening or 5–9pm (15.8%). Only 9.1% reported peak drug use occurring during the day. Bivariate comparisons showed that intermediate types (79.7%) and evening types (76.9%) were more likely than morning types to report this later time for most frequent drinking (9pm onwards). However, almost two-thirds (64.7%) of morning types did report this 9pm-or-later time. Further, bivariate comparisons showed that reporting the later time of 9pm onwards was more common among gay men (vs. bisexual), while daytime use was endorsed by more partnered than single men. Men endorsing peak use between 5–9pm were, on average, older than those endorsing daytime or later-than-9pm use. In multivariable analyses displayed in Table 2, after adjusting for covariates, only chronotype significantly predicted the time of peak club/party drug use,.

The demographic characteristics of the sample utilized for Hypothesis 3 are displayed in Table 3. Excluding the 186 men with no recent alcohol use, the 927 men with recent alcohol use had a mean age of 40.8 (SD = 13.5), and were mostly White (61.5%). On average, evening types (28.5%) were younger (M = 36.7, SD = 12.3) than morning types (M = 49.0, SD = 13.0; 20.9%) and intermediate types (M = 40.7, SD = 13.2; 50.6%), F(2, 1110) = 63.7, p < 0.001. The majority (53.1%) of the 927 men reported using alcohol to help stay awake—218 (23.5%) indicated use of both alcohol and alcohol mixed with energy drinks to do so, while 153 (16.5%) reported alcohol only and not energy drinks, and 121 (13.1%) reported drinking alcohol with energy drinks but not alcohol alone. Combining these, almost one-third of morning types (32.0%) endorsed this motivation—however, bivariate comparisons showed that intermediate types (41.2%) and evening types (43.9%) were more likely to do so. Comparisons showed that men endorsing this motivation were, on average, younger and were more likely to be Latino or Multiracial/Other. In Model 1 in Table 4, younger age, being Latino or Multiracial/Other, and higher income were positively associated with endorsing this motivation, while chronotype was not. Additionally, men endorsing this motivation for alcohol use also had higher AUDIT scores than men not endorsing this motivation, adjusting for age and chronotype—Exp(B) = 1.21, 95%-CI: 1.15, 1.27, p < 0.001.

Overall, 26.9% of the 401 men with recent club/party drug use reported having used drugs to help stay awake. Almost one-fifth of morning types (19.4%) endorsed this motivation, while 25.5% of intermediate types and 33.6% of evening types did so. Demographic comparisons showed that men endorsing this motivation were, on average, younger. In Model 2 in Table 4, younger age and being White or Black were positively associated with endorsing this motivation, while chronotype was not. DAST items were completed by only 119 men who reported recent use—and on average, the 83 of these men who endorsed this motivation for drug use had higher DAST scores than those who did not, adjusting for age and chronotype—Exp(B) = 1.67, 95%-CI: 1.26, 2.22, p < 0.001.

Our findings highlight the relevance of time-of-day and tiredness in understanding substance use behaviors, here in relation to GBM who remain at elevated risk of problematic substance use and adverse outcomes related to substance use (namely, HIV), and who also tend to experience comparatively poor sleep quality compared to heterosexuals (Chen & Shiu, 2017; Galinsky et al., 2018; Patterson et al., 2018). Our findings provide support for Hypothesis 1, that alcohol and club/party drug use can both be considered as primarily nighttime activities for the vast majority of the GBM we surveyed. Indeed, very few men reported that drinking (2.5% of men) and club/party drug use (9.1% of men) most frequently occurred during the day. Identifying nighttime as the most likely time for substance use accords with the findings of Shiffman’s (2009) review. Further, multivariable analyses showed that both younger age and a later chronotype were associated with increased odds of reporting the later-than-9pm time for drinking, while only chronotype was associated with the later time for club/party drug use. This may be due to any number of lifestyle factors among younger GBM such as employment (e.g., working later shifts) or timing preferences for social activities and norms amongst friends, and concurs with Dawson’s (1996) study which showed that younger adults more commonly report later times of drinking.

In support of Hypothesis 2, times of most frequent alcohol and club/party drug use differed according to chronotype, even when adjusting for age differences between the three chronotype groups. While morning types were more likely to report earlier times for drinking and drug use, a still-substantial number of morning types reported drinking (33.2%) and drug use (64.7%) most often from 9pm onwards. This is important because, by this time of night, it can be expected that the typical morning person would be feeling tired or at least “not in their prime” (see Schmidt et al., 2007). This suggests that many men are not at their optimal level of cognitive and emotional functioning when choosing whether to drink or use drugs, and how to manage their rate of use. Furthermore, the later it gets, the more tired they are expected to become and additionally, the more intoxicated they are likely to be from previous use. The role of circadian misalignment in substance use therefore warrants further investigation.

Our findings also support Hypothesis 3. A majority of alcohol-using GBM (53.1%) reported sometimes using alcohol (whether with or without energy drinks) to help them stay awake if they are out at night and are feeling tired, while 26.9% of drug-using GBM endorsed the same motivation for drug use. In other words, tiredness is a factor that can situationally motivate substance use in a substantial proportion of GBM. Further analyses showed that younger age was associated with increased odds of reporting this motivation for both alcohol and drug use, which is concerning given that rates of problem drinking and drug use are also more pronounced among younger GBM compared to their heterosexual counterparts (Marshal et al., 2008). Finally, use severity scores (AUDIT and DAST) were higher for those endorsing this motivation for use of alcohol and drugs to stay awake.

Previous studies on the use of energy drinks mixed with alcohol have suggested that energy drinks are frequently used to counter the sedative effects of alcohol and to lift energy (Snipes & Benotsch, 2013; Wells et al., 2013). Our findings extend this by showing that a substantial proportion of GBM reported drinking alcohol without energy drinks to help them stay awake longer, which resonates with the work of Hendler et al. (2013) regarding the stimulatory effects of alcohol alone. We contend that the experience of being tired and the wish to stay awake longer combine to constitute a motivation for many GBM that increases their substance use, and therefore that this motivation should be counted amongst motives for use (alongside enhancement motives; Cooper et al., 1992). This work extends the focus of existing models of substance use behavior which rely on stable, person-level, cognitive variables (e.g., beliefs, knowledge, personality traits), by also acknowledging the fluctuating influence of physiological processes such as tiredness and circadian rhythms.

We propose that sleep health interventions to increase one’s awareness of the effects of tiredness and to address poor sleep—which was recently named a “public health epidemic” (CDC, 2015), and especially so for sexual and gender minority individuals (Chen & Shiu, 2017; Galinsky et al., 2018; Patterson et al., 2018)—could help to prepare GBM with greater alertness, cognitive functioning, and emotion regulation when making their decisions about substance use. Also, future research could explore indirect pathways from tiredness to substance use via intervening factors such as impaired emotion regulation, increased cravings, or negative affect.

Limitations of the current work include the brevity of the measures used and the generalizability of the samples. Greater precision regarding the exact times of most frequent substance use would be informative, as the current study was unable to determine exactly how late use may be occurring. It should also be noted that we only asked about time of most frequent use and not about concurrent levels of tiredness in each event. More nuanced information about tiredness in-the-moment of making substance use decisions could be gleaned from studies involving ecological momentary assessment and actigraphy monitoring. More information on lifestyle factors (e.g., employment, socioeconomic status, neighborhood characteristics) may be relevant—in particular, whether the individual is a shift-worker or on a nocturnal schedule. The social context for use—i.e., whether the substance use is occurring at home in private or socially in more public settings—should also be explored as a factor in substance use for sexual and gender minority individuals, given connections to “nightlife,” and community or “scene” participation. Pressure from peers and/or partners regarding substance use and staying awake also warrants attention. More comprehensive measures of chronotype and circadian misalignment would be advantageous in future research. Future research could also explore the demographic differences noted in our analyses—e.g., that the later drinking time was more common in younger men, single men, GBM of color, and those from the hookup app and Facebook. Finally, we expect that similar dynamics may apply to other populations of interest, and would encourage future research in this direction.

In essence, this work has uncovered the possibility that, at times, GBM drink or use drugs when they are tired and perhaps do so because they are tired, to the further detriment of their self-regulatory capacities. Evidently, this spiral suggests a complex dynamic between tiredness and substance use which—though challenging on a study design level—highlights the need for research to employ appropriately complex time-sensitive methodologies. Further research is needed to examine whether the lateness of the hour when substance use occurs might be affecting the decisions that individuals are making about whether to have another drink or hit, or whether to engage in other health-compromising behaviors such as sexual risk-taking (which also commonly occurs at night; e.g., Millar, Starks, Rendina, & Parsons, 2018), eating fast food, or driving while intoxicated. Exploring the temporal patterns of substance use among GBM (as well as other populations) and their intersection with chronotype and thus circadian misalignment, offers new and valuable knowledge regarding risk factors in substance use and could help to develop interventions to improve the individual’s ability to manage their substance use and associated behaviors.