This study was conducted to determine the possible radiopharmaceutical potential of morphin labeled with I-131. Morphine was extracted from dry capsules of the opium poppy (Papaver somniferum L.), purified by high-performance liquid chromatography, and characterized with nuclear magnetic resonance and infrared spectroscopy. The purified compound was labeled with I-131. Male Albino Wistar rats (18) were used for receptor blockage and unblockage biodistribution studies. Tissue distribution studies showed that radiolabeled morphine had higher uptake in lung, liver, small intestines, large intestines, and stomach than the other tissues. The highest uptake of radiolabeled compounds in rats' brain was found to be in the midbrain and hypothalamus. After receptor blockage with morphine, uptake of I-131-morphine decreased in the lungs, liver, kidney, testis, prostate, spinal cord, cerebellum, hippocampus, striatum, and temporal cortex with respect to receptor unblockage studies of rats. This study concludes that the labeling yield of I-131-morphine was high, high amount of I-131-morphine was found in the hypothalamus, and I-131-morphine has enough stability for diagnostic scanning.