The photluminescence intensity and morphology of zinc oxide (ZnO) nanowires have shown inherent instability under high light intensities. We present scanning electron microscope (SEM) results that indicate accumulation of morphological changes under strong light exposure. In ZnO microstructures, one typically finds a strong enhancement of the luminesence intensity up to some optimum annealing time, followed by a decrease as illumination continues. Here we show that a similar metastable behavior applies to the threshold and intensity of random lasing in ZnO nanoparticle films.