Cannabinoids induce apoptosis on glioma cells via stimulation of ceramide synthesis de novo, whereas they do not affect viability of primary astrocytes. In the present study, we show that incubation with Delta9-tetrahydrocannabinol did not induce accumulation of ceramide on astrocytes, although incubation of these cells in a serum-free medium (with or without cannabinoids) led to stimulation of ceramide synthesis de novo and sensitization to oxidative stress. Thus treatment with H2O2 induced apoptosis of 5-day-serum-deprived astrocytes and this effect was abrogated by pharmacological blockade of ceramide synthesis de novo. The sensitizing effect of ceramide accumulation may depend on p38 mitogen-activated protein kinase activation rather than on other ceramide targets. Finally, a protective role of cannabinoids on astrocytes is shown as a long-term incubation with cannabinoids prevented H2O2-induced loss of viability in a CB1 receptor-dependent manner. In summary, our results show that whereas challenge of glioma cells with cannabinoids induces accumulation of de novo -synthesized ceramide and apoptosis, long-term treatment of astrocytes with these compounds does not stimulate this pathway and also abrogates the sensitizing effects of ceramide accumulation.