* Aconitum napellus: Also called wolfsbane or monkshood, this flowering plant is highly toxic and can cause respiratory failure and death.
* Atropa belladonna: Better known as deadly nightshade, this evergreen perennial contains atropine and scopolamine, which can cause delirium, hallucinations, and even death.
* Conium maculatum: Sometimes called hemlock, this flowering plant can cause paralysis and respiratory failure. It was famously used to execute the Greek philosopher Socrates.
* Digitalis purpurea: Also known as foxglove, this ornamental flowering plant contains a substance that can affect the heart rate and cause death if ingested in high doses.
* Strychnos nux-vomica: The seeds of this tropical evergreen tree are highly poisonous and can cause vomiting, seizures, and respiratory failure.
* Arsenic: A naturally occurring element that was often used as a poison in Shakespeare's time. Arsenic poisoning can cause gastrointestinal problems, vomiting, and death.
* Mercury: A heavy metal that was once used to treat syphilis, mercury poisoning can cause kidney damage, brain damage, and eventually death.
It's worth noting that Shakespeare was writing in a time before modern medical knowledge, and his understanding of poisons was based on the knowledge available to him at the time. Some of the substances he mentions may not be considered poisonous today, or may have different effects than he described.