The greatest number of participants rated positive reinforcement or “pleasure seeking” as a very important motivation for their drug use, with a smaller but generally non-overlapping group reporting “pain avoidance” or negative reinforcement as a very important motivation for drug use. Many of those identifying positive reinforcement as important also rated stimulus-response learning, incentive salience, or inhibitory control dysfunction as important, suggesting that the obvious motivation of pleasure seeking frequently co-exists with other, perhaps equally relevant, reasons for using drugs. This overlap has been emphasized previously in theoretical papers on addiction,11,35
but, to our knowledge, has not been tested in clinical models of addiction. Surprisingly, however, participants rating positive reinforcement as very important to their drug use also reported that they continued to enjoy other activities as well. Ratings on this scale did not correlate with depressive symptoms, either. This is at odds with the idea that chronic drug exposure produces dysfunction in brain reward systems rendering users less able to enjoy other activities,36
though we could not directly test that hypothesis in this study.
Among those rating negative reinforcement highly, less than half also reported that drugs lessen withdrawal symptoms. This was unexpected, as this aspect of negative reinforcement seems critical for theories of addiction based on opponent-process concepts.4
According to negative reinforcement theory, drug use is motivated by withdrawal symptoms that are reversed by drug use early in the addictive process, but later they are only partially and transiently reversed by drug use. A minority of our participants rated negative reinforcement or withdrawal as important to their ongoing drug use. This was unexpected, as methamphetamine has a long elimination half-life,37
produces marked changes in brain dopamine,38
and has been reported to produce withdrawal symptoms.24,25
The stimulus-response learning model was rated highly by a substantial subgroup of participants. This group described their drug use as habitual and thoughtless. This is consistent with theories of aberrant learning,39
which purports that drug-seeking behavior progresses from an “action-outcome” stage, in which reinforcing effects control behavior, to a habit stage, in which stimulus-response associations take over control. Addiction is conceived of, in part, as habitual responding that is relatively insensitive to the value of the reward. One fifth (20%) of our participants identified drug taking as having prominent habitual characteristics.
Impairments in inhibitory control, or more broadly, impulsivity,16,17
is another conceptualization of addiction with a strong basis in neuroscience research.20,22
About a quarter of our participants reported that impaired inhibitory control plays a role in ongoing drug use and relapse. Impulsivity is a multi-dimensional construct, including such concepts as perseveration, acting in the absence of forethought, and undue risk-taking.40
Further work is needed to characterize the aspects of impulsivity that participants believe are most important.
Incentive salience or “craving” was rated highly as a motivation for drug use and relapse by the smallest number of participants, a finding at odds with common conceptualizations of addiction.41–43
Strikingly, 36% believed that craving contributed not at all to their drug use, and a majority (55%) did not believe that objects associated with drug use produced cravings. Explanations for this contradictory finding could include the suggestion that participants have a response bias against reporting craving, that they are unaware of cravings, or that they themselves define craving idiosyncratically and do not attribute relevant feeling to the word “craving.” Clinical experience suggests that some subjects, for example, identify craving with specific somatic experiences, and would use the words “desire” or “want” to express what we referred to as craving. If this were so, participants might have rated this item differently if we had used the word “want” rather than “crave.” On the other hand, the modest magnitude of cue-induced increases in craving seen in experimental studies has generally not been appreciated. For example, in a large study in this area,44
about one-third of 150 cocaine-dependent volunteers did not report any
increase in craving following exposure to cocaine cues. In another study,45
among those reporting increases in craving the magnitude of increase averaged 3.4 points out of 10.45
This frequency and magnitude of craving may not be sufficient to account for a great deal of drug use. This is consistent with a recent qualitative study that found that most methamphetamine users did not perceive craving as insurmountable.46
By contrast, in clinical trials craving has been shown to significantly predict subsequent drug use,27,47,48
suggesting that there may well be an important role for craving as an important motivation for drug use. This issue clearly requires further investigation.
The results from the correlation and factor analysis suggest that positive and negative reinforcement reflect different constructs, with the other constructs being related somewhat to each. This suggests that concepts associated with the other theories of addiction are needed for a comprehensive understanding of participants’ perceived motivations for using methamphetamine.
Depressive symptoms, indexed by the BDI, were positively associated with ratings for the first question each category, excepting positive reinforcement, which did not correlate with the BDI. This suggests that depressive symptoms may contribute to negative reinforcing and incentive effects of drugs, and may play a role in impulsive drug use. This also suggests that people reporting they use drugs for their pleasurable effects do so irrespective of self-reported depressive symptoms.
Results from this study support the contention that methamphetamine users may be more heterogeneous than is often appreciated, and imply that treatment development might be more successful if aimed at particular subtypes of patients.42,49
A formidable challenge is identifying valid subgroups of users. Further research is needed to define coherent subgroups of users that could guide the development of individualized treatments for methamphetamine dependence. In addition, it is unclear whether subgroups, if they could be identified reliably, would be stable over time. Nevertheless, results from this study indicate that users identify a range of motivations for using drugs, suggesting that further research in this area would likely contribute to advances in treatment development research.
In the absence of external validation, a key limitation of this survey approach is that we sampled participants’ opinions regarding reasons for using methamphetamine and did not employ questionnaires with established reliability and validity. Although the instrument had substantial internal consistency as evidenced by the high Cronbach alpha level, this report must serve as preliminary evidence of the usefulness of this novel instrument. The potential pitfalls of self-report instruments are well known.50
A further limitation of these findings includes the under-representation of women and minority racial and ethnic groups among methamphetamine users in West Los Angeles, the area where the survey was conducted. Nevertheless, this initial attempt to characterize responses of self-identified subgroups of methamphetamine dependent volunteers may inform treatment development research by facilitating the identification of more homogenous subgroups of patients. This may facilitate the identification of treatments with differing degrees of efficacy for different subgroups of patients.42,49,51