Complex sentence: Historically, most cases of nicotine poisoning have been the result of use of nicotine as an insecticide, whereas more recently poisoning typically appears to be due to accidental ingestion of tobacco or tobacco products or ingestion of nicotine containing plants.
Split into simpler sentences: Historically, most cases of nicotine poisoning have been the result of use of nicotine as an insecticide. Whereas more recently poisoning typically appears to be due to accidental ingestion of tobacco or tobacco products or ingestion of nicotine containing plants.