Prescription opioids are widely used for chronic low back pain (cLBP) in the US.1,2 Many concerns have been raised regarding opioid prescribing, including addictive potential, misuse, and accidental overdose.3–6 Several studies have shown that a history of illicit drug use is associated with prescription opiate misuse.7–10 Little is known about the prevalence of illicit drug use in Americans with cLBP.
Hence, we set out to determine the extent of illicit drug use in community-based US adults with cLBP. Our primary objective was to compare the prevalence of illicit drug use among US adults with cLBP and those without cLBP. In addition, we wanted to know whether prescription opioid use was associated with a history of illicit drug use among cLBP sufferers.
MATERIALS AND METHODS
We analyzed data from the continuous National Health and Nutrition Examination Survey (NHANES), a biannual research survey conducted by the National Center for Health Statistics to assess the health and nutritional status of the US population. The survey combines household interviews with physical examinations, conducted at mobile examination centers. The NHANES methodology generates a research sample that is representative of the US population.11 During the 2009 to 2010 NHANES cycle, a comprehensive back pain questionnaire was administered with the primary goal of establishing the prevalence of inflammatory back pain in US adults.12 The questionnaire included all adult participants ages 20 to 69 years (N = 5103). We identified the cLBP sample from participants who reported current pain in the area between the lower posterior margin of the ribcage and the horizontal gluteal fold at the time of evaluation with a history of pain lasting almost every day for at least 3 months (N = 700). To be classified as having cLBP, participants had to answer “yes” to two questions: “Was there one time when you had pain, aching or stiffness almost every day for 3 or more months in a row?” and “Do you still have pain, aching or stiffness?”. We merged the back pain survey data with the NHANES questionnaires on illicit drug use and prescription medication use, as well as demographics, income, occupational history, tobacco, and alcohol use.
The drug use questions focused on lifetime and current use of marijuana or hashish, cocaine, heroin, and methamphetamine. Questions were self-administered in a private setting, using the Audio Computer-Assisted Self-Interviewing system. Current drug use was defined as at least one instance within the last 30 days. Results for marijuana and hashish use were available on all participants up to age 59. For all other substances, results were available on the full sample (up to age 69). For estimates of high-risk alcohol use behavior, we provide a modified Audit-C score, as for question 3, NHANES asked about five or more drinks per day, rather than six or more drinks per day as in standard Audit-C.13
Primary sample unit (“sdmvpsu”) and stratum (“sdmvstra”) variables, as well as 2-year interview weights (“wtint2yr”) were used to obtain national estimates for household questionnaire variables, and 2-year MEC weights (“wtmec2yr”)—for MEC variables. Chi-square test and one-way analysis of variance (ANOVA) were used for unadjusted between-group comparisons of categorical variables and continuous variables, respectively. Logistic regression was used to produce adjusted odds ratios for the primary binary outcome (cLBP). As heterogeneity of demographic characteristics was observed in the groups with and without cLBP, logistic regression models were adjusted for age, race, gender, and education level.
To determine whether lifetime and current illicit drug use were associated with prescription opioid analgesic use, we performed two subgroup analyses in the cLBP group, in which we compared the proportions of subjects with active opioid prescriptions stratified on lifetime and current illicit substance use. A 95% confidence level was set for all tests of significance. All statistical analyses were performed in SAS 9.4 (SAS Institute, Inc., Cary, NC).
Demographic characteristics by cLBP status are summarized in Table 1. The point prevalence of cLBP in US adults aged 20 to 69 years old was 13.1%. US adults with cLBP were older than those without cLBP, with the age distribution skewed toward the fifth and sixth decades of life. There were more women in the cLBP group than in the non-cLBP group (55.8% vs. 50.1%, P = 0.036), and more Caucasians (74.9% vs. 64.9%, P < 0.0001). Adults with cLBP were less educated, with 18.6% reporting a college degree or higher, compared with 30.2% of those without cLBP (P = 0.0001).
The distribution of illicit drug, alcohol, and tobacco use among US adults overall, and according to cLBP status, is summarized in Table 2. The prevalence of lifetime use of any illicit drug (marijuana, cocaine, heroin, or methamphetamine) was 49.0% in the cLBP group, and 43.3% in the non-cLBP group, aOR 1.42 (1.12–1.79), P = 0.0035. The prevalence of current illicit drug use in the past 30 days was also higher in the cLBP group: 14.2% compared with 9.3% among those without cLBP, AOR 1.91 (1.34–2.73), P = 0.0004. In addition, adults with cLBP were significantly more likely to smoke tobacco: aOR 1.44 (1.12–1.86) for former smokers and 1.77 (1.37–2.30) for current smokers, P = 0.0001. Although a trend for increased alcohol use was observed in the cLBP group, there was no statistically significant difference after adjustment for age, race, gender, and education: aOR 1.21 (0.96–1.52), P = 0.114. In addition, no difference was observed in the prevalence of high-risk alcohol behavior by modified AUDIT-C among subjects with and without cLBP.
We further examined illicit drug use prevalence by substance (Table 3); adjusted odds ratios are shown in Figure 1. For lifetime use, marijuana was the most commonly reported drug in US adults, followed by cocaine, methamphetamine, and heroin. About 46.5% of subjects with cLBP reported lifetime marijuana use, compared with 42% of subjects without cLBP: aOR 1.36 (1.06–1.74), P = 0.016. About 21.9% of those with cLBP reported lifetime cocaine use, versus 13.9% of those without cLBP: aOR 1.80 (1.45–2.24), P < 0.0001. Methamphetamine use was reported by 9.2% of subjects with cLBP and 4.6% of subjects without cLBP: aOR 2.03 (1.30–3.16), P = 0.0019. Heroin use was 5% in the cLBP group and 2.1% in those without cLBP: aOR 2.43 (1.44–4.11), P = 0.0009. Similar patterns were observed for current substance use within the last 30 days.
We evaluated prescription opioid analgesic use within the cLBP group in two subgroup analyses (Figure 2). Subjects with cLBP who reported lifetime illicit drug use were more likely to have an active prescription for opioids than subjects with cLBP who did not use illicit drugs: 22.5% versus 15.3%, P = 0.018. Among current illicit drug users with cLBP, 25.7% had an active prescription for an opioid analgesic versus 17.7% of current nonusers with cLBP; this difference, however, was not statistically significant, P = 0.250.
After accounting for heterogeneous demographic characteristics, lifetime and current illicit drug use (including specific use of marijuana, cocaine, heroin, and methamphetamine) were each associated with the presence of cLBP among a representative sample of community-dwelling US adults aged 20 to 69 years. Among adults with cLBP, those with a history of lifetime illicit drug use were more likely to have an active prescription for an opioid analgesic than cLBP sufferers without an illicit drug use history.
Our general population estimates for illicit substance use were consistent with the national population surveys from the same years (2009–2010).14 The prevalence of illicit drug use in the US has increased since 2010, especially among adults in their 50s and 60s, the age group with the highest prevalence of back pain in our study.15 Few previous studies have examined the association of illicit drug use with cLBP among adults living in the US. A 1996 family medicine clinic study from Madison, WI, found no difference in lifetime substance abuse between patients with cLBP (N = 61) and without (N = 181) in the 18 to 59-year age group; this study, however, used phone interviewing to collect substance abuse information.16 The National Comorbidity Survey Replication from 2001 to 2002 also reported no association between self-reported drug abuse problems and chronic spinal pain, in a US nationally representative sample that included older adults.17 Only a fraction of illicit substance users, however, self-identify as having abuse problems, or have clinically documented addiction.15 It is also plausible that the prevalence of illicit drug use increased disproportionately in the cLBP population compared with the general population over the past two decades. For example, a series of urine toxicology studies by Manchikanti et al.18,19 from the early 2000s showed a higher prevalence of illicit substance use in a pain management clinic setting, with 11% of urine samples positive for marijuana, over 6% positive for cocaine, and 3% positive for amphetamines in patients on stable doses of opioids, and 32% of urine specimens positive for illicit substances in patients seeking higher doses of opioids. Similarly, a 2008 large urine toxicology study from pain clinics in six states reported urine samples positive for marijuana in 8.9% of chronic pain patients, cocaine in 2.8%, and amphetamines in 1.5%.20 The prevalence of opioids in the urine was 82% in this sample. These studies did not differentiate between chronic pain diagnoses and were not designed to compare drug use rates with the general population.
Our study's strengths include a large nationally representative sample, and private computer-based drug use questionnaire administration, that is less susceptible to reporting bias than other interviewing methods. However, this study has several limitations. NHANES is a cross-sectional survey, with many self-report variables that are subject to measurement error and recall bias. Temporal relationships and causality cannot be established from this study design, and, as with any observational study, residual confounding is likely present. Data collection was limited to subjects between 20 and 69 years of age; thus, results should not be extrapolated on younger and older subjects. The study only included the noninstitutionalized population, and may be undersampling populations at a high risk of illicit drug use.
The association between a history of illicit drug use and prescription opioid use in the cLBP population is consistent with previous studies,21,22 but may be confounded by other clinical conditions. Mental health disorders, for example, have been associated with both illicit substance use and prescription opioid use in the cLBP population.23,24 In the context of management, however, illicit drug abuse is predictive of aberrant prescription opioid behaviors.7–10,25 As we face a prescription opioid addiction epidemic,26 careful assessment of illicit drug use history may aid prescribing decisions.
Our study did not differentiate between recreational and medical marijuana use. With the expanding acceptance of marijuana use in the US, the relationship between prescription opioid use and marijuana may become more complex. While at the time of this survey 14 states had medical marijuana laws in place,27 by 2015, the number of states with medical marijuana laws increased to 23.28 Studies of medical marijuana for cLBP remain limited, with low quality of evidence on effectiveness and adverse events.29
Despite the limitations, our study offers insights into an important public health problem of drug abuse in the cLBP population, and has the advantage of using a nationally representative sample of community-dwelling adults. Further evaluation of illicit drug use as a predictor in longitudinal studies of cLBP will facilitate a deeper understanding of the relationships between pain, illicit substance use, and prescription opioid administration, and assist in the design of safe and sustainable interventions for patients with chronic pain.
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Keywords:Copyright © 2016 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.
chronic pain; cocaine; epidemiology; heroin; illicit drugs; low back pain; marijuana