Etiology of Sinusoidal Obstruction Syndrome Common causes include Irradiation Graft-vs-host disease resulting from bone marrow or hematopoietic cell transplantation Pyrrolizidine alkaloids in crotalaria and senecio plants (eg, medicinal bush teas) and other herbs (eg, comfrey) Other hepatotoxins (eg, dimethylnitrosamine, aflatoxin, azathioprine, some anticancer drugs) Pearls & Pitfalls Ask patients who have cryptogenic liver abnormalities about use of herbal and natural products (including bush and herb teas) and anabolic steroids (which can cause peliosis hepatis).