The toxin present at the highest level in the seeds of Cycas revoluta is cycasin.
Cycas revoluta, commonly called the sago palm or king sago, is a cycad rather than a true palm. All parts of the plant are toxic, but its seeds contain the highest concentration of cycasin. The seeds can therefore be especially dangerous to people and animals that mistake them for edible plant material.
Cycasin is a carcinogenic and neurotoxic glucoside. In the digestive tract, it can be converted into methylazoxymethanol, a reactive compound that damages cells and DNA. Poisoning may cause vomiting, diarrhea, weakness, seizures, and severe liver injury.
The name “sago palm” can cause a second misconception: edible sago is usually palm starch, whereas starch from cycads requires careful repeated processing to remove toxins. Cycasin is also found in other cycads, including Zamia species, and is not the same toxin as BMAA, another neurotoxic compound associated with cycads.