To provide phenothiazine or a phenothiazine analog or derivative (phenothiazine material) in the form of prills of a generally spherical shape containing very low levels of fines and a method for forming the phenothiazine material in the form of prills of a generally spherical shape.

The product in a prill form preferably contains 99.6% of phenothiazine. The method includes dividing a fluid of the fused phenothiazine material into a plurality of droplets of a uniform size to form a solid phenothiazine material in the form of prills and cooling the droplets while keeping an inert gas atmosphere until the droplets is cooled to 140°C or lower.