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Introduction: Lateral flow assay method is a test for rapid detection of morphine that h-as many applications in identification of ad-dicts. However, detection level of the sys-tem has limited its application. This rese-arch examined how to improve the detec-tion level and sensitivity of this system. Materials & Method: pH of conjugation, OD of conjugated material and concentr-ation of morphine-BSA in the test band w-ere effective on the detection level of this system. To determine optimum pH, a com-mercial kit (Gold in a box) was used. By applying various concentrations of morp-hine solution, and considering a constant concentration of morphine-BSA, the opt-imal OD was set. Then, the optimal conc-entration of morphine-BSA was obtained for a fixed amount of OD. Effect of block-ing the conjugated pad and addition of su-gar to the conjugated substance were also studied. Findings: Optimum values of pH and OD was pH=8.4 and OD=1. Optimum conce-ntration of morphine-BSA in the test band was obtained to be 0.5 mg/ml. Cut-off value of optimized kit attained to 25 ng/ml. After comparing the results with a standard kit, sensitivity and specificity of the optimized kits were 100 % and 99% , respectively. Discussion & Conclusion: Finding and opt-imizing the effective factors on the perf-ormance of diagnostic lateral flow method can be an effective strategy to increase the sensitivity and reduce the detection level of this system.