To date, the understanding of PTSD’s association with medication adherence has been confounded by its association with depressive symptoms. We aimed to determine whether this would be the case for a group of individuals who were at high risk for PTSD and who had a strong need to adhere to medication to prevent future catastrophic health events, namely stroke and TIA survivors from diverse communities. We found that, indeed, elevated symptoms of PTSD were common in stroke or TIA survivors up to 5 years after their most recent stroke or TIA, with 18% of participants having symptoms consistent with a likely PTSD diagnosis and nearly 3 out of 4 participants with elevated symptoms of PTSD. Furthermore, stroke/TIA survivors with likely PTSD had nearly three times the risk of medication non-adherence in adjusted analyses, and the association between PTSD and medication adherence remained significant even after controlling for depressive symptoms. Furthermore, even participants with more modest elevations in PTSD symptoms were at increased risk of medication non-adherence, broadening the relevance of this risk factor for non-adherence to a large number of stroke/TIA survivors.
A large percentage of participants in our sample (41%) were non-adherent according to the Morisky questionnaire. For comparison, in the Adherence eValuation After Ischemic stroke–Longitudinal (AVAIL) Registry, only 14% of participants self-reported being non-adherent to medications.(30
) In the AVAIL study, low socioeconomic status was associated with lower adherence. Hence, the high prevalence of patients from low socioeconomic background may help explain the higher prevalence of non-adherence in our sample.
Prior studies assessing the relationship between PTSD triggered by acute medical events and medication non-adherence have not always found an independent association after adjusting for covariates.(10
) There are several possible explanations for why our results differed. First, we had a relatively large sample size and a high proportion of participants were non-adherent to medications. These factors increased our statistical power to detect independent associations in multivariable analyses. However, the large magnitude of the relative risks we found suggest that power was not the only difference between our study and previous investigations.
The severity of PTSD may have been higher in our post-stroke/TIA sample as compared to other populations.(31
) Our finding that symptom severity is associated with medication non-adherence suggests that greater PTSD severity in our sample may account for the difference between our findings and previous studies. Strokes and TIAs may be especially conducive to PTSD as a result of the acute, frightening nature of the stroke/TIA-related symptoms.
Finally, the fact that the triggering event for the PTSD symptoms was a medical event as compared to other sources of trauma may have resulted in a distinct association between PTSD and self-management of medical illness. For example, one of the defining clusters of PTSD symptoms is avoidance of reminders of the triggering event. Accordingly, when symptoms of PTSD are triggered by medical events, PTSD may cause patients to avoid stroke medications if they serve as reminders of the PTSD-inducing event.
A number of other potential mechanisms might explain the relationship between PTSD and medication non-adherence. PTSD has been directly associated with deficits in cognitive function both in patients with and without traumatic brain injury.(32
) Accordingly, cognitive dysfunction may be a mechanism linking PTSD with medication non-adherence due to forgetfulness or other cognitive factors. Some investigators have hypothesized that participants with elevated PTSD symptoms may hold different beliefs about treatment that may impact on medication adherence.(34
) Wagner et al. showed that among African American HIV-infected individuals, perceived discrimination by the health care system partially mediated the relationship between PTSD and non-adherence to antiretroviral medications.(35
) Given the high proportion of participants at risk for discrimination in our sample on account of their minority and low income status, it would be important to test this mechanism in future studies. This mechanism, however, may not be generalizable to other patient populations.
There were several limitations to the interpretation of our findings. The cross-sectional nature of the data prevents us from ascribing causal attributions to the association of PTSD to medication adherence. The recruitment of a high proportion of minorities from low socioeconomic backgrounds and of individuals who were motivated to participate in an educational workshop may have limited the generalizability of the study’s findings to other populations. The PCL-S and PHQ-8 measure symptoms of PTSD and depression, respectively, but these do not replace diagnoses based on a psychiatric interview. Further, a modified version of the PCL-S was used and this may have influenced its discriminant properties. Nevertheless, we used the most conservative cutpoint for categorizing participants as having likely PTSD and may have underestimated the true prevalence of PTSD diagnosed by a psychiatric interview. Medication adherence was measured using self-report and no objective measures of adherence were available to confirm responses. Although the Morisky has been validated with objective adherence measures in other studies, patients tend to over-report how well they adhere to medications such that the prevalence of poor adherence to medications may be underestimated by this study.