The list of the most dangerous poisons are given in the below article.
Cyanide of one of the most dangerous poison those results to a condition of Asphyxia and kills by avoiding the RBC oxygen saturation. Strychnine is another dangerous poison that is dangerous as well as most popular and it attacks the nervous system and leads to severe reflex reactions.
Though Arsenic is present in very little quantity in all the human tissues but when it is used in the form of poison it leads to diarrhea with blood, vomiting and gastric disorders. Snake Venom is another poison and biting of snake can lead to failure of the organs, pain at the bitten site and swelling.
The poisonous nature of Hemlock is due to Cicutoxin, alcohol and polyyne and its one bite can cause death of an adult.
Heroin is another poison that is very powerful as it affects the respiratory system and develops a feeling of euphoria and lowers the central nervous system. The tetraodontoxin present in the ovaries of Pufferfish is poisonous in nature.
Another dangerous poison is the venom of Fiddleback Spider and its bite will lead to swelling, vomiting, acute state of confusion and necrosis. Belladonna leaves and Castor plant seeds are also poisonous in nature.