The World Health Organization defines adherence as “the extent to which a person’s behavior – e.g., taking medication, following a diet, and/or executing lifestyle changes – corresponds with agreed recommendations from a health care provider” (1). Adherence to medication includes initiation (e.g., the first intake of the drug as prescribed), implementation (e.g., the extent of medication intake compared to medically prescribed dosage), and discontinuation (e.g., ceasing medication for any reasons (2);. Nonadherent behavior can manifest in several ways. For example, patients may decide not to take their medication at all, take it at different times than prescribed, or take incorrect dosages (e.g., under-dosing and over-dosing). They may also interrupt therapy indefinitely or discontinue treatment altogether (3). Several risks are associated with poor medication adherence, including relapses and potential rehospitalization, as well as delayed remission with a reduced quality of life (1). Consequently, nonadherence poses a significant barrier to effective medical treatment in the 21^st century. Chronic diseases, in particular, require long-term medication adherence to improve prognosis and quality of life. However, various studies have indicated that the average adherence rate among patients with chronic illnesses (e.g., hypertension and diabetes mellitus) is approximately 50% (1, 4–6). Hence, approximately half of those with adequate access to healthcare do not follow medical instructions to optimize their health. Moreover, the rate of nonadherence among patients with chronic psychiatric conditions is even higher (7–9), with 74% of this patient group discontinuing prescribed medication within 18 months for various reasons (e.g., side effects and perceived inefficacy (10);). Despite these general trends, relatively little research has examined medication adherence in individuals with obsessive-compulsive disorder (OCD). According to the ICD-10 (11), this psychiatric condition is characterized by two primary criteria: recurring intrusive ideas, thoughts, or impulses (e.g., obsessions) and repetitive actions (e.g., compulsions), which are both associated with a high level of distress or dysfunction. Most affected individuals recognize the senselessness of their symptoms due to persistent insight during the course of the illness. The associated shame may delay initial contact with the psychiatric system and, consequently, the initiation of effective therapy (12). A previous study demonstrated that the average duration between symptom onset and diagnosis is 12.78 years. Following diagnosis, an additional 1.45 years typically pass before the initiation of treatment (13).

Guideline-recommended treatment approaches for OCD include both cognitive-behavioral therapy (CBT) with exposure and response prevention (ERP) and pharmacotherapy with selective serotonin reuptake inhibitors (SSRIs) as first-line treatments, which can be used individually or in combination depending on patient preference, symptom severity, or accessibility (14). Participants receiving antipsychotic augmentation were classified as treatment-resistant based on clinical judgment and their pharmacological regimen, although no formal staging criteria were applied. In line with previous findings (15, 16), supporting the efficacy of augmentation with risperidone and aripiprazole – and to a lesser extent quetiapine – the addition of one of these agents to an SSRI was considered a valid augmentation strategy. Few studies have systematically evaluated medication adherence in OCD, particularly with regard to influencing factors, individual support strategies, and patient resources. This study aimed to evaluate medication adherence in patients with OCD through indirect (questionnaire-based) and direct (TDM-based) methods, assess attitudes toward pharmacotherapy, and explore individual strategies for supporting adherence.

The results of this study provide a unique insight into medication adherence in people with OCD, a frequently underrepresented population in adherence research.

In the present study, the participants reported mild impairments in psychological, social, and occupational functioning despite the presence of clinically significant OCD symptoms (18, 28). Obsessive thoughts and checking were the most common while washing, hoarding and neutralizing, whereas washing, hoarding, and neutralizing were less frequently reported. The combination of moderate GAF scores and clinically relevant OCI-R scores indicated that, although individuals functioned relatively well in daily life, OCD symptoms continued to cause substantial distress and interfered with everyday activities.

In light of these findings, understanding adherence to prescribed pharmacological treatments becomes essential. Most participants (over 80%) were prescribed SSRIs, and a smaller subset (17.4%) received antipsychotic augmentation. Previous research has shown that antipsychotic augmentation (e.g., quetiapine, risperidone, or aripiprazole) may improve treatment outcomes in OCD that is refractory to treatment (29–32). Current treatment guidelines distinguish between combination strategies and augmentation. While antipsychotic augmentation (e.g., with aripiprazole or risperidone) is formally recommended after insufficient response to SSRI or clomipramine monotherapy, combining an SSRI with clomipramine is typically considered after multiple failed monotherapy trials and is supported by lower evidence strength, while also posing the risk of clinically severe drug interactions (14).

One-fourth (24.4%) of the participants reported good medication adherence, 62.2% reported partial adherence, and 13.4% reported nonadherence based on self-reported questionnaire data. No significant change was observed in adherence levels over a one-year period, which indicated a stable pattern of adherence behavior within that timeframe. Consequently, approximately three-quarters of the participants did not take their medication as prescribed (i.e., partial or nonadherence). This finding is consistent with previous research, which has shown that 50% or more of patients in long-term psychiatric treatment either fail to fully adhere to their regimen or discontinue medication entirely (33–35). Interestingly, participants who were undergoing pharmacological augmentation differed significantly from the rest of the sample in both overall medication attitudes (DAI) and self-reported adherence (MARS). Notably, this difference was primarily driven by the subscale Attitude toward taking medication, suggesting greater ambivalence among those receiving augmentation. While actual adherence behavior did not differ significantly, the more negative attitudes in this group may reflect perceptions of treatment chronicity, reduced outcome expectations, or internalized stigma – particularly given the association of antipsychotics with more severe psychiatric conditions. Previous research has shown that internalized stigma is a critical factor that negatively impacts medication adherence, particularly in patients with OCD (36, 37). Higher levels of self-stigma are significantly correlated with lower adherence, likely because stigma and misconceptions about psychiatric disorders act as barriers to seeking and completing treatment. Taken together, these findings underscore the importance of addressing both emotional and cognitive responses to complex treatment regimens, as well as implementing stigma-reduction strategies to improve adherence and optimize long-term outcomes – especially in patients with treatment-resistant OCD.

Interestingly, 84.6% of the participants for whom TDM was available had drug levels within the therapeutic range, while only 15.4% had subtherapeutic levels. TDM is an objective measure of adherence, but it may not always correlate perfectly with self-reported medication behavior due to factors such as irregular dosing, metabolic variability, or individual differences in drug absorption and pharmacokinetics (25, 38, 39). In the present study, both individuals with subtherapeutic levels reported partial adherence and only moderately positive medication attitudes. This pattern reflects a clinically plausible profile – where medication is not entirely rejected but instead is taken inconsistently or without full conviction. Such cases highlight the nuanced continuum between behavioral and attitudinal adherence, and underscore the utility of TDM as a complementary tool to detect suboptimal intake that may otherwise remain undetected by self-report alone. The overall high proportion of therapeutic drug levels in this subgroup may also indicate optimized dosing and pharmacological monitoring, which may mitigate side effects and enhance adherence (39, 40).

The study also revealed significant concerns among participants regarding their prescribed medication. Notably, no significant difference was found in DAI-10 scores during the one-year follow-up investigation. Approximately 24.4% were dissatisfied with their current pharmacological treatment, while 72.1% were unsure whether it would prevent relapse and improve cognitive function. While the effects of SSRIs on cognition remain unclear and the results are inconsistent at present (41–43), SSRIs have been shown to reduce symptoms and prevent relapse (44). Long-term use of SSRIs can stabilize symptoms, reduce the likelihood of relapse, and improve quality of life (45–47). However, many participants (55.8%) strongly believed that medication is only necessary during acute illness episodes. Particularly concerning are previous findings showing an association between lower positive drug attitudes and poor adherence (48). Poor adherence alone can lead to symptom relapse, increased hospitalizations, and elevated suicide risk (49–51). Therefore, addressing these attitudinal and belief-based barriers is crucial for improving medication adherence and preventing long-term negative outcomes.

Regarding adherence predictors, no significant relationship was found between sociodemographic factors (e.g., age, gender, and education) or clinical factors (e.g., duration from symptom onset to diagnosis, GAF score, and OCI-R score). This finding is consistent with the existing literature, which suggests that sociodemographic factors are generally inconsistent predictors of adherence in psychiatric populations (33, 52). In contrast, certain clinical factors, such as symptom severity and illness duration, have demonstrated predictive value in other studies (53–55), highlighting the need for a more nuanced approach that considers a broader range of psychosocial variables (e.g., insight into illness, social support, and treatment beliefs or credibility).

Strategies to improve adherence primarily involve behavioral modification. The participants supported strategies such as coupling medication intake with daily activities (e.g., meals and bedtime routines). These approaches highlight the role of habit formation in reducing the cognitive load associated with remembering to take medication (56, 57, 58). In addition, the consistent timing of medication intake, particularly for psychopharmaceuticals, may enhance treatment effectiveness by reinforcing routines (59–61). However, external monitoring strategies (e.g., filming medication intake) have been largely rejected. Recent research suggests that while digital tools can be beneficial, overly invasive methods may diminish patients’ sense of autonomy and create discomfort (62–64).

This study investigated medication adherence in individuals with OCD, a group often underrepresented in research. The findings revealed that partial adherence was relatively common. The participants experienced significant OCD symptoms and moderate impairments in various life domains despite receiving appropriate treatments such as SSRIs and, in some cases, augmentation with antipsychotics.

The study underscores the potential of TDM not only as a tool for optimizing pharmacotherapy and improving adherence in complex cases, but also for objectively detecting suboptimal medication intake that may not be captured by self-report. Nevertheless, TDM results may not always perfectly align with actual medication behavior due to various influencing factors. Participants’ notable concerns about medication side effects and doubts regarding efficacy highlight the importance of directly addressing these issues to improve adherence.

Behavioral strategies (e.g., integrating medication intake into daily routines) are promising for enhancing adherence by leveraging habitual behavior and aligning medication schedules with circadian rhythms. However, external monitoring methods, perceived as intrusive, are less favorably received.

This study underscores the importance of personalized, adaptive approaches to treatment and adherence in OCD, emphasizing the role of TDM, patient education, and the establishment of supportive routines that both empower patients and address their concerns about medication.