While usually due to aspirin, other possible causes include oil of wintergreen and bismuth subsalicylate.[1] Excess doses can be either on purpose or accidental.[2] Small amounts of oil of wintergreen can be toxic.[2] Diagnosis is generally based on repeated blood tests measuring aspirin levels and blood gases.[1] While a type of graph has been created to try to assist with diagnosis, its general use is not recommended.[1] In overdose maximum blood levels may not occur for more than 12 hours.[2]