A clinically significant response to endoxifen in compulsive buying behavior emerging in a patient with long-standing obsessive-compulsive disorder

INTRODUCTION

Compulsive buying behavior (CBB) is characterized by repetitive, uncontrollable purchasing leading to distress or functional impairment. Although once conceptualized primarily as an impulse-control disorder, contemporary frameworks consider it within the obsessive–compulsive and related disorders spectrum due to overlapping phenomenology such as anxiety-driven urges and relief-seeking behaviors.^1,2 CBB has been linked to serotonergic, dopaminergic, and reward-processing dysregulations.³

Comorbidity of CBB with obsessive-compulsive disorder (OCD) adds diagnostic complexity, as clinicians may misinterpret the behavior as a variant of compulsions, impulse-control dysfunction, or behavioral addiction. Evidence-based pharmacological options remain limited. Mood stabilizers, selective serotonin reuptake inhibitors (SSRIs), and cognitive-behavioral interventions have produced variable outcomes.⁴

Endoxifen, an active metabolite of tamoxifen, has emerged as a potential agent targeting protein kinase C (PKC) pathways and serotonergic modulation, showing benefits in impulsivity-related symptoms in emerging literature.⁵ However, reports of its use in compulsive buying remain scarce.

We present a case demonstrating significant improvement in treatment-resistant compulsive buying in an OCD patient following the introduction of endoxifen. The case is intended to add to the sparse therapeutic evidence and offer clinical insights for psychiatrists encountering similar challenges.

CASE REPORT

A 45-year-old male with a documented 20-year history of OCD presented with a new-onset pattern of compulsive buying over the past year. His primary OCD symptoms included intrusive contamination fears, repetitive washing, prolonged bathing rituals, and frequent checking for correctness. The patient remained stable for several years on fluoxetine 80 mg/day and clomipramine 75 mg/day, with adequate functioning and no prior history of behavioral addiction.

DISCUSSION

Compulsive buying is an underrecognized behavioral condition frequently overshadowed by more classical OCD symptoms, especially when both occur concurrently. Clinicians often debate whether such buying is a compulsion, an impulse, or a reward-driven addictive act. In this patient, the behavior clearly aligned with CBB, characterized by tension before purchases, transient relief afterward, and progressive functional impairment, consistent with previous descriptions in the literature.¹ Differential diagnostic considerations included antidepressant-induced bipolar spectrum disorder (Bipolar III), particularly in view of the patient’s long-term treatment with high-dose fluoxetine and clomipramine. However, the absence of lifetime hypomanic symptoms such as elevated or expansive mood, decreased need for sleep, increased energy, grandiosity, pressured speech, or episodic mood shifts argued against a bipolar spectrum diagnosis. The compulsive buying behavior was characterized by anxiety-driven urges, mounting inner tension, and transient relief following purchase rather than pleasure-seeking, euphoric mood, or goal-directed excess typically seen in hypomanic impulsivity. Furthermore, thepatient had tolerated high-dose antidepressants for several years without affective switching, and the onset of compulsive buying behavior was insidious rather than temporally related to antidepressant initiation or dose escalation. These clinical features support the conceptualization of the behavior as compulsive buying within the obsessive-compulsive spectrum rather than bipolar impulsivity. Nevertheless, bipolar spectrum disorders remain an important differential diagnosis in patients presenting with new-onset impulsive behaviors, and careful longitudinal assessment is essential.²

CONCLUSION

This case illustrates the emergence of compulsive buying behavior as a distinct and impairing symptom in a longstanding OCD patient and highlights the potential role of endoxifen in its management. The significant and rapid improvement observed suggests that endoxifen may be a promising option for treatment-resistant compulsive buying. Larger studies are needed to understand the mechanisms and establish evidence-based guidelines. Early identification of CBB and timely intervention can prevent financial, interpersonal, and psychosocial consequences.