The most frequently occurring adverse effects were nausea, vomiting, headache, and fatigue. Most adverse effects were self limiting, and the nausea and vomiting were controlled with antiemetics. The incidence of grade 3 or 4 nausea occurred in 10%, and vomiting occurred in 6%. The dose-limiting toxicity of temozolomide is myelosuppression. The median nadirs in temozolomide studies occurred at 28 days (range 1 to 44 days) for neutrophils and 26 days (range 22 to 40 days) for platelets. The myelosuppression is the most common dose-limiting adverse event. The average time for the absolute neutrophil count (ANC) and platelet count to return to normal from the nadir was 14 days. Temozolomide may induce hypercoagulability. Pulmonary emboli and venous thrombosis were observed however, it is possible those events may have been associated with the disease being treated rather than the treatment.