Overdosing often occurs among patients with borderline personality disorder (BPD) and confronts physicians with the dilemma of whether to prescribe psychotropic agents for them or not. Prescribing psychotropic agents is often unavoidable in the real world, because psychotherapy alone is sometimes insufficient to control their labile emotions. We report two cases of BPD in which overdosing was successfully prevented by changing the dosage form from tablets to a powder and adding a bitter taste to make it difficult to swallow a large dose at one time. Prevention of overdosing by BPD patients definitely requires a comprehensive treatment approach in terms of its social, biological, psychological, and psychopathological aspects. Although no perfect method of preventing overdosing is currently available, our method provides an option when psychotropic agents are prescribed for BPD patients in clinical practice.