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Craving, defined as the subjective experience of an urge or desire to use substances, has been identified in clinical, laboratory, and preclinical studies as a significant predictor of substance use, substance use disorder, and relapse following treatment for a substance use disorder. Various models of craving have been proposed from biological, cognitive, and/or affective perspectives, and, collectively, these models of craving have informed the research and treatment of addictive behaviors. In this article we discuss craving from a mindfulness perspective, and specifically how mindfulness-based relapse prevention (MBRP) may be effective in reducing substance craving. We present secondary analyses of data from a randomized controlled trial that examined MBRP as an aftercare treatment for substance use disorders. In the primary analyses of the data from this trial, Bowen and colleagues (2009) found that individuals who received MBRP reported significantly lower levels of craving following treatment, in comparison to a treatment-as-usual control group, which mediated subsequent substance use outcomes. In the current study, we extend these findings to examine potential mechanisms by which MBRP might be associated with lower levels of craving. Results indicated that a latent factor representing scores on measures of acceptance, awareness, and nonjudgment significantly mediated the relation between receiving MBRP and self-reported levels of craving immediately following treatment. The mediation findings are consistent with the goals of MBRP and highlight the importance of interventions that increase acceptance and awareness, and help clients foster a nonjudgmental attitude toward their experience. Attending to these processes may target both the experience of and response to craving.

Over the past decade, substance use disorder has been conceptualized as a chronic relapsing condition (McLellan, 2002 and McLellan et al., 2005), where relapse has been variously defined as either the return to problematic substance use following treatment or as a process of behavior change (Brownell et al., 1986, Maisto et al., 2003 and Witkiewitz and Marlatt, 2004). A substantial amount of research over the past 20 years has focused on identifying predictors of relapse and developing treatments (including pharmacological and psychological) that may help prevent relapse. One of the strongest predictors of relapse to emerge in both pre-clinical and clinical research studies is craving (Anton, 1999, Breese et al., 2011, Drummond, 2001, Marlatt, 1978, Shadel et al., 2011 and Sinha and O'Malley, 1999), and many of the promising pharmacotherapies and most effective psychotherapies for addiction have focused on reducing or managing substance craving. In the current paper, we review the efficacy of mindfulness-based relapse prevention as a treatment for substance use disorders and empirically examine mechanisms of action for reduction of substance craving. 1.1. Substance craving The concept of “craving” as an essential facet of substance use disorders is generally accepted by researchers, clinicians and patients, yet operational and conceptual definitions vary widely (Anton, 1999, Potgieter et al., 1999, Rosenberg, 2009, Skinner and Aubin, 2010 and Tiffany et al., 2000). Skinner and Aubin (2010) reviewed 18 models of craving that have emerged over the past 60 years, and concluded that while collectively the models of craving have been indispensible in the research and treatment of addictive behaviors, none of the models independently provide a complete explanation of the craving construct. For the purposes of the current paper, we define craving as the subjective experience of an urge or desire to use substances. Consistent with numerous models of craving, we acknowledge that it can be experienced as intrusive thoughts and their elaboration (Kavanagh et al., 2006), an impulsive drive or motivation (Cox & Klinger, 2002), substance wanting (Robinson & Berridge, 1993), an emotional state (Tiffany & Wray, 2009), a physical sensation (Paulus, 2007), a stress response (Sinha & Li, 2007), or any other manifestation that is salient for an individual who endorses experiencing “craving” or an “urge” to use substances. The roots of craving can be attributed to biological, affective, or cognitive motivators. Within biological models of craving, addiction is viewed as a brain disease, and the etiology of substance craving and substance use are both born out of neurobiological and physiological states (Robinson and Berridge, 1993 and Wise, 1988). Craving can be reflected in neural states, as suggested by studies linking neurotransmitters such as dopamine, serotonin, and gamma-aminobutyric acid (GABA) to drug use (Johnson et al., 1992 and Wise, 1988) and/or alcohol use (Addolorato et al., 2005b and Verheul et al., 1999). For example, dopamine in the dorsal striatum has been associated with reported craving (Volkow et al., 2006), and GABA dysregulation has been associated with a craving drive described as a relief of tension (Addolorato, Abenavoli, Leggio, & Gasbarrini, 2005). Other biological models of craving focus on physiological withdrawal states, wherein craving can occur as interoceptive dysregulation (Goldstein et al., 2009 and Paulus and Stein, 2006). Affective models suggest that craving is an emotion that can be elicited by affective expectancies, negative affect or stress (Baker et al., 1986 and Wikler, 1948). In terms of positive expectancy, craving for drug use is elicited with positive associations with the effects of drug use. With negative affect, craving is suggested to be a state elicited by the avoidance of negative affect or stress associated with withdrawal such that craving can be both the result and cause of stress (Sinha & Li, 2007). Thus, the core motivation to avoid negative affective states is the cause of craving (Baker, Piper, Fiore, McCarthy, & Majeskie, 2004). In support, stress- and negative-affect-induced states have been shown to increase craving in the laboratory (Sinha & O'Malley, 1999). Further, negative affect is one of the most frequently endorsed reasons for relapse (Brownell et al., 1986 and Marlatt and Gordon, 1985). Within an affective model of craving, affective states can elicit craving or prevent individuals from inhibiting craving. From a cognitive perspective, it is suggested that craving is rooted in cognitive processes (e.g., memory, expectancies) that reflect higher-order information processing (Tiffany, 1999) that evolve into automatic processes of use (Tiffany, 1990). For example, Marlatt posits that craving is a result of cognitive expectancies for drug use (Marlatt, 1978 and Marlatt and Gordon, 1985). Stress-induced craving is an example of how cognitive interpretations of an event can trigger craving, even in a laboratory setting (Sinha & Li, 2007). Additional evidence suggests that self-efficacy is a critical factor in the relation between craving and substance use (Marlatt & Witkiewitz, 2005). Hence, cognitive models of craving clearly outline craving as a psychological process, separate from drug use, whereby craving can occur without substance use, and substance use can occur without craving (Skinner & Aubin, 2010). While these perspectives provide unique explanations of the causes of craving, many specific models of craving are a complex amalgam of biological, affective and cognitive constructs. For example, the withdrawal model (Wikler, 1948) describes craving, or the drive to use, as a result of both a biological conditioned response to drug related stimuli, and an attempt to escape negative affective states. Additionally, the theory of neural opponent motivation identifies craving as a biological deviation from the homeostatic regulation of neurotransmitters that can be elicited by change in affective states (Koob and Le Moal, 2001 and Koob and Le Moal, 2008). Different perspectives on craving imply unique implications for treatment. A cognitive perspective of craving treatment might target working memory (Houben, Wiers, & Jansen, 2011) or re-training attention to push substance cues away (Wiers, Rinck, Kordts, Houben, & Strack, 2010). An affective process perspective might focus on disrupting the association between negative affective states and the desire to use. A neurobiological perspective would be interested in directly targeting neurobiological dysfunction to impact craving (Volkow et al., 2006). 1.2. A mindfulness perspective on craving A fourth perspective on craving, of particular interest to the present study, comes from the mindfulness literature, and the use of mindfulness-based treatments to reduce and cope with craving. Such a perspective has the potential to advance the conceptualization and the treatment of neurobiological, cognitive, and affective aspects of craving. Mindfulness has been described as, “the awareness that emerges through paying attention, on purpose, in the present moment, and nonjudgmentally to the unfolding of experience” (pg. 145; Kabat-Zinn, 2003). While secularized in most Western treatment contexts, mindfulness meditation has roots in the Buddhist tradition. From a Buddhist perspective, craving is considered a core component of human existence, and craving and attachment are viewed as the root cause of human suffering (Bodhi, 2005). From a mindfulness perspective, we might view addiction as an effort to either hold on to or avoid cognitive, affective or physical experiences. In an effort to avoid suffering, an individual either clings onto positive states (e.g., craving the next high) or avoids negative states (e.g., seeking an escape from sadness). Mindfulness practice includes observing craving, which is considered to be a transient cognitive and affective phenomenon, just like any other experience. Thus, the intention of the practice is to bring awareness to the experience of craving and to learn to observe it without reacting and without judgment. Another intention of mindfulness practice is to increase acceptance of one's experience, allowing one to experience his or her current physical and affective state as impermanent. In recognizing that neither positive nor negative states are enduring, an individual realizes that the effort exerted to achieve or cling to a particular state of being is not only futile, but causes suffering. The practice of accepting physical and affective states as they are in the present moment is counter to the clinging quality of craving (Breslin, Zack, & McMain, 2002). Finally, the practice of mindfulness meditation has been shown to reduce neural aspects of craving (Westbrook et al., 2011). Specifically, Westbrook et al. (2011) found that the brain regions that are typically activated during craving (including the subgenual anterior cingulate cortex) showed reduced activity during mindful attention of smoking images, as compared to looking at the smoking images without mindful attention. Furthermore, during mindful attention, there was significantly reduced functional connectivity between the subgenual anterior cingulate cortex and other regions associated with craving, including the ventral striatum and the bilateral insula. Taken together, there is evidence to suggest that mindfulness-based treatment has the potential in addressing neurobiological, cognitive, and affective aspects of craving. 1.3. Mindfulness-Based Relapse Prevention Drawing from the Buddhist tradition, Marlatt (2002) recognized that craving and addiction could be targeted by mindfulness meditation, but that many individuals might need additional cognitive and behavioral skills for coping with high risk situations for relapse. In response to the need for integrating mindfulness meditation with cognitive–behavioral skills training for addiction, Mindfulness-Based Relapse Prevention (MBRP; Bowen et al., 2010 and Witkiewitz et al., 2005), was developed as an aftercare treatment program that was designed to reduce the risk and severity of relapse following intensive substance abuse treatment. 1.3.1. The Mindfulness-Based Relapse Prevention program The MBRP program consists of eight 2-hour sessions, each including formal mindfulness practices, as well as exercises and skills designed to bring these practices into daily life, specifically into situations in which an individual is at high risk for relapse. The first three sessions focus on raising awareness of environmental triggers, and the physical, affective and cognitive reactions that follow, bringing awareness to the progression of reactions that occur in response to such cues. Clients learn “informal” mindfulness practices based on the foundational meditation practice they have built thus far to step out of the habitual cognitive and behavioral patterns and choose a more skillful response. As early as session two, clients engage in exercises specifically focused on coping with craving. Through in-session exercises designed to elicit craving, clients practice bringing awareness to the multiple components of their experience while slowly increasing exposure and intensity to the craving response. They practice approaching the reactions with a gentle curiosity, and are given instructions to guide them through “staying with” the experience without exacerbating it, giving into it, or attempting to suppress it. The exercise allows clients to practice imaginal exposure and nonreactivity to substance use triggers. They learn skills to stay in contact with the internal reactions to external triggers (i.e., craving in response to substance use cues) that put them at high risk for relapse. Additionally, they learn an alternative, competing response to craving by approaching the experience with curious awareness, deescalating the process by not engaging in habitual cognitive or behavioral patterns that tend to intensify the craving reaction. In order to increase ability to tolerate the discomfort often associated with craving and other reactions to triggers, clients maintain an ongoing practice of both formal meditation and of exercises designed to increase awareness of triggers and reactions. They begin to increase their ability to endure the affective and physical discomfort without reacting in ways that may temporarily relieve distress, but lead to problematic longer-term outcomes. The final two sessions of the course focus on social and environmental factors that either support or detract from the maintenance of treatment gains and an ongoing mindfulness practice. 1.3.2. Pilot randomized trial of Mindfulness-Based Relapse Prevention A randomized pilot trial was conducted to assess feasibility and establish initial efficacy of the MBRP treatment protocol (Bowen et al., 2009). Participants (N = 168) were clients from a private, nonprofit treatment agency providing a continuum of care to adults with alcohol or other drug use disorders. To be eligible for the study, individuals had to have completed either inpatient or intensive outpatient treatment, and be medically stable to progress into aftercare. As such, all participants had completed initial treatment immediately prior to entering the trial, and were thus in early stages of abstinence. Clients with psychotic disorders or acute suicidality were excluded from participating. Following a web-based baseline battery of assessments, participants were randomized to either MBRP or to treatment as usual (TAU) as delivered by the agency, which consisted primarily of 12-step treatment and psychoeducational programming. Analyses in the parent study (Bowen et al., 2009) revealed a difference in racial distribution between groups at baseline, with a higher percentage of White participants in MBRP (63%) than TAU (45%). This difference was a not a systematic effect of randomization; thus, race was used as a covariate in all analyses in the parent study (Bowen et al., 2009). There were no other baseline differences between groups in demographic or main outcome variables. Overall, this indicates that randomization was successful. Following the 8-week treatment period, participants randomized to the MBRP condition returned to their regular agency aftercare programs. As described in more detail in Section 2, assessments were given at baseline, immediately following the 8-week treatment period, and 2 and 4 months following the treatment. Individual characteristics, psychosocial factors and substance use in the 60-day period prior to entering initial inpatient or intensive outpatient treatment were assessed. MBRP and TAU participants reported using substances on 27 (SD = 24) and 28.9 (SD = 24.8) days, respectively (Bowen et al., 2009). This difference was not statistically significant. With respect to substance use outcomes, participants in both groups had a low base rate of substance use during and following treatment, with average days of use over the follow-up of 9.33 days for TAU (SD = 20.80) and 5.62 days for MBRP (SD = 14.33). Across both groups, fewer than 30% of participants (29.1% in TAU, 28.6% in MBRP) had any days of use. Of those who used, 28.6% and 33.3% of TAU and MBRP participants, respectively, only used substances on one day during the follow-up period. A curvilinear effect of treatment on substance use outcomes suggested that treatment gains made by MBRP participants, compared to TAU participants, decayed by 4 months post-treatment. Analyses of craving showed a significantly greater decrease over the 4-month follow-up period in MBRP participants as compared to those in TAU. Additionally, there were significant increases in acceptance, as measured by the Acceptance and Action Questionnaire (Hayes et al., 2004), in MBRP versus TAU participants. Secondary analyses of data from the study by Bowen et al. (2009) found individuals who received MBRP were less likely to experience craving in response to depressed mood and the attenuated reactivity to depressed mood and reduced craving also predicted fewer days of substance use for those who received MBRP (Witkiewitz & Bowen, 2010). Based on these findings, we hypothesized that MBRP may extinguish the habitual response of subjective craving during periods of negative mood. Yet, previous studies have not examined mechanisms by which MBRP might reduce craving or alter the response of craving during negative mood states. Given the basic tenets of MBRP, we propose numerous factors may predict levels of self-reported craving and changes in craving over time following MBRP. As noted above, one of the primary goals of MBRP is to target both the experience of and response to craving. Through several exercises and practices, clients increase their awareness of triggers that elicit craving and of the “automatic” craving reaction in response to these triggers. They practice acceptance of the discomfort often associated with triggers that may have, in the past, led to craving for escape relief, such as a desire for a substance to decrease the intensity of the negative affective, cognitive, or physical state. Finally, clients practice relating to their experiences and reactions with a nonjudgmental attitude, decreasing the distress often associated with self-judgment, frustration or shame in relation to craving or use. We hypothesize that awareness, acceptance and nonjudgment function as necessary and interdependent processes, each supporting one another, and each an essential factor in the mitigation of the craving response. For example, awareness is a necessary condition for acceptance, i.e., an individual cannot truly accept something of which he or she is not aware. However, an individual may be aware of his or her experience but unwilling or unable to accept it. This individual may be more likely to attempt to deny or suppress the experience of craving, which may in turn result in even greater craving (Berry, May, Andrade, & Kavanagh, 2010). Finally, an individual may be aware of an experience, such as an affective response to a substance use trigger, but may experience self-judgment or shame about the reaction, increasing levels of negative affect and thus putting the individual at greater risk of increased craving. Thus, we hypothesized that a latent factor indicated by acceptance of experience, acting with awareness, and a non-judgmental attitude toward inner experience, would predict lower levels of craving and would mediate the association between receiving MBRP and changes in craving over time. 1.4. Current study The goal of the current study was to follow-up on the significant effect of MBRP on post-treatment craving scores reported by Bowen et al. (2009) by examining theoretically driven mechanisms of change. The first goal of the current study was to examine the effect of MBRP on levels of craving and changes in craving over time in a latent growth modeling framework to estimate the between-person and within-person variability in craving scores over time. The second goal was to build upon the study by Bowen et al. (2009) by examining whether changes in acting with awareness, acceptance, and nonjudgment, mediated the association between participation in MBRP and self-reported changes in craving during and following MBRP.