National Trends in the Use of Antidepressants Between 1997 and 2009 and the Role of Medicare Part D Implementation

Depression is a common chronic disorder that affects all age groups of the United States population (1). Because of the distress and the poor physical condition that often accompany depressive symptoms, persons with depression have low quality of life (2). As a result, their use of health care and expenditures for health care are higher than for people without depression (3). Thus proper treatment for depression is important to improve patients’ well-being and to help reduce health care use and spending. Antidepressant medications are commonly recommended as a treatment for depressive symptoms (4).

During the 1990s and early 2000s, there was a nationwide trend toward increasing use of antidepressant treatment. Studies from nationally representative samples reported that antidepressant use among persons who received outpatient treatment for depression increased from 37% in 1987 to 75% in 2007 (5,6). This significant increase was attributed in part to the introduction of newer antidepressants, such as selective serotonin reuptake inhibitors (SSRIs), which are safer and have fewer side effects than traditional tricyclic antidepressants (TCAs) (7). In addition, the use of direct-to-consumer advertising of antidepressant medications was found to be associated with the initiation of the treatment (8).

Building on this prior literature, our study used data from 1997 to 2009 to examine more recent national trends in the use of antidepressants among people with depression. In particular, our analysis encompassed the implementation of Medicare Part D, which provides prescription drug coverage to Medicare beneficiaries and is expected to increase the consumption of prescription drugs. This major policy change, which took effect in 2006, has had the potential to affect antidepressant utilization, particularly among Medicare beneficiaries. To date, little is known about national trends in antidepressant treatment after Part D.

Chen and others (9) examined the impact of Part D on antidepressant use among Medicare beneficiaries; however, the study’s analysis was limited to 2006, the initial year of Part D. Another study reported that between 2004 and 2007, antidepressant utilization increased by 61% among Medicare beneficiaries who gained prescription drug coverage through Part D (10). However, the sample was limited to Part D enrollees of a single managed-care plan.

Our study analyzed trends in antidepressant use in nationally representative samples between 1997 and 2009. Moreover, we characterized patterns of antidepressant treatment by insurance source, which so far has not been examined in the literature. We also assessed whether antidepressant treatment after Part D was significantly different among Medicare beneficiaries than among people covered by other types of insurance.

Methods

We used multiyear data (1997–2009) from the Medical Expenditure Panel Survey Household Component (MEPS-HC), which includes five rounds of interviews over two and a half years involving a nationally representative sample of noninstitutionalized U.S. residents (11). The data include information on health care utilization (type, frequency, expenditure, and payer) and sociodemographic characteristics of respondents and their families.

We identified individuals with depression by using MEPS-HC medical conditions files. The survey asks respondents to describe their medical conditions. From this self-reported information, professional coders recorded individuals’ medical conditions by using the International Classification of Diseases, ninth revision, Clinical Modification (ICD-9-CM). Persons with ICD-9-CM codes 296 or 311 recorded for any round of interviews was defined as having had depression during that calendar year (12).

The MEPS-HC prescribed medicines file provides self-reported information on medication use. We identified antidepressants by drug names, including TCAs (amitriptyline, amoxapine, clomipramine, desipramine, doxepin, imipramine, maprotiline, mirtazapine, nortriptyline, and protriptyline); SSRIs (citalopram, escitalopram, fluoxetine, fluvoxamine, paroxetine, and sertraline); and others (bupropion, duloxetine, nefazodone, selegiline, trazodone, and venlafaxine) (12). We constructed a binary variable representing whether the respondent had at least one of these medications during a calendar year.

A key variable of the analysis was insurance coverage. We categorized the type of insurance into four mutually exclusive groups: Medicare, Medicaid, dual coverage for Medicare and Medicaid (dual eligible), and private coverage. We excluded uninsured people, whose pattern of health care service use may be so different from that of insured populations as to make ready comparison difficult.

Covariates used in the analysis were age, race (white, black, and Hispanic), gender, education, family income, and health risk. The education variable was classified as zero to 12 years, 13 to 15 years, and 16 or more years. Family income was grouped as ≤124% of the federal poverty level (FPL), 125%−199% of the FPL, 200%−399% of the FPL, and 400% or more of the FPL. Health risk was measured by chronic condition indicators and the number of prescription drugs taken by a patient. [Descriptive statistics of all covariates reported by insurance group are available online in a data supplement to this report.]

We analyzed the trends in antidepressant use over time by using logistic regression controlling for sociodemographic factors. We included dummy variables for year to capture the trend in treatment between 1997 and 2009. Using 1997 as the base year, we obtained the adjusted odds ratios (AORs) of antidepressant use for all subsequent years. The analysis was conducted for each insurance group. Standard errors were clustered within an individual in all analyses to account for repeated interviews of the individual that occurred because of the panel survey design.

Next, we examined the effect of Part D on the use of antidepressants among Medicare beneficiaries by estimating a logistic model with an interaction term between the Part D and Medicare indicators. The Part D indicator equaled 1 if the year was 2006 or after and 0 if the year was before 2006. The Medicare indicator equaled 1 if the patient was covered by Medicare and 0 if not. Our main interest was the coefficient of this interaction, which indicated whether the changes in antidepressant use after Part D were significantly different among Medicare beneficiaries than among other groups. This is known as the difference-in-difference (DD) estimator. We obtained DD estimates for Medicare and all other insurance groups combined as well as for Medicare and each of the other three insurance groups. We controlled for all patient characteristics, and we adjusted standard errors for clustering within an individual.

Results

The percentage of people using antidepressants increased in all insurance groups between 1997 and 2009. The Medicare group had a large increase in 2006 but showed a somewhat stable trend after that, while the privately insured group had a consistent increase from the early 2000s up to 2009. The Medicaid group showed a relatively slow increase compared with the other insurance groups. [A figure depicting unadjusted trends in antidepressant use by insurance coverage is available online as a data supplement to this report.]

Table 1 presents the results of a regression analysis of the trend in use of antidepressants by insurance group. The estimates by year dummies indicated increasing use of antidepressants during the study period in all groups. The odds of use of antidepressants in the Medicare group significantly increased in 2006 relative to 1997 (AOR=2.52), potentially reflecting the impact of Part D. However, AORs remained relatively stable from 2007 through 2009 (between 2.69 and 3.30). The odds of antidepressant use increased significantly in the Medicaid group starting in 2005 and in the dual-eligible group starting in 2004. AORs in the private coverage group increased continuously from 2002 up to 2009 and reached their highest levels in 2008 (AOR=4.81) and 2009 (AOR=6.63).

For other covariates, older people were more likely than younger people to take antidepressants in the Medicaid and private coverage groups. Whites had significantly greater odds of using antidepressants than blacks in the Medicare and privately covered groups. The effects of education and income were mostly insignificant.

Table 2 shows the results from the regression examining whether use of antidepressant treatment after Part D increased more in the Medicare group than in the other groups. With Medicaid as the control group, the analysis indicated that the interaction term between Part D and Medicare indicators was significant (AOR=1.35). This implies that the increase in the odds of taking antidepressants after Part D was significantly larger among Medicare beneficiaries than in the Medicaid group. The interaction term in other analyses was insignificant.

Discussion

The use of antidepressants between 1997 and 2009 increased in all insurance groups. This overall increasing trend is encouraging; however, our analysis indicates that the rate of utilization and the degree of the increase over time differed by insurance group. The Medicaid group showed a lower rate of utilization and a slightly slower increase in utilization over time than were seen in other groups. Our study did not explore reasons for these differences or the appropriateness of utilization in each group. However, the assessment of the treatment pattern is the first step toward ensuring the use of effective services. Further research is necessary to assess the need for antidepressant treatment and the level of appropriate use in each insurance group.

Our analysis showed that Part D led to a greater use of antidepressants among Medicare beneficiaries, compared with the Medicaid group. This positive effect of Part D on antidepressant treatment is consistent with the prior literature (9,10). However, the large increase seems to have occurred mostly during the initial year of Part D, which suggests that further evaluations of Part D are needed to better understand its long-term impact.

We did not find a significant increase in the use of antidepressants among Medicare beneficiaries after Part D compared with dual-eligible or privately covered populations. This suggests that there may have been interventions to improve antidepressant use in those non-Medicare groups during the post–Part D period. Identifying mechanisms through which other insurance (non-Medicare) groups improved drug utilization is an important topic for future research.

A few limitations of the study should be noted. First, we relied on self-reported medical conditions to identify patients with depression, which raises a concern that receiving antidepressant treatment was a determinant of self-reporting depression. If this were the case, we would have observed an increase in the number of people with depression but little or no increase in the rate of antidepressant use. However, our data indicate that the depression population did not grow as antidepressant use increased over time, suggesting that such a concern was unlikely.

Second, our analysis was limited to the insured population. The use of depression treatment is likely to be low among the uninsured, a population that needs extensive attention and interventions. However, we excluded persons without insurance because they may exhibit systematically different characteristics that do not allow for appropriate comparison with the insured.

Third, although MEPS is a methodologically rigorous survey, it is subject to reporting errors, potentially because of recall problems among the respondents. However, there is no conclusive evidence that those errors systematically differ among insurance groups or change over time, and the impact of reporting errors on our findings of the trends, if any, was likely to have been insignificant.

Conclusions

The use of antidepressants among people with depression increased continuously in all insurance groups up to 2009. Increases after Part D were larger among Medicare beneficiaries than among Medicaid beneficiaries. The different patterns of utilization and trends over time among insurance groups suggest that further research is needed to explore the reasons for those differences and to assess levels of appropriate use of antidepressants by insurance group.