Hemlock (Conium maculatum L.)
Because of its association with the death of Socrates, hemlock (Conium maculatum L.) is one of the most recognized botanicals in ancient medicine. Ancient populations were very aware of hemlock and its poisonous nature. Every school child seems to know about Socrates and hemlock. There is even an old joke that "Socrates was a wise man, a kind man who gave people advice and then they poisoned him." This third essay in the series will describe hemlock not in terms of its historical importance but will discuss its active components, mode of action and medicinal uses in ancient medicine.
Hemlock is a member of the order Umbelliferae that also includes carrots, parsnips and fennel, as well as the now extinct silphium. The plant is a biennial and is tall, highly branched with excellent foliage and white flowers but has a bitter taste and unpleasant odor when bruised. This has likely prevented accidental overdoses. Hemlock produces a large number of seeds, which then allow it to form large stands in a variety of soil types. In addition to the obvious issue with human consumption, there are substantial concerns about the consumption and toxicity or teratogenicity observed when animals, especially horses, cattle and other domestic animals, consume the plant.
Eight piperidine alkaloids have been identified in hemlock. The alkaloids are a group of mildly alkaline compounds, usually of botanical origin, that can produce strong physiological effects. As a class over 3000 alkaloids have been recorded. Of the eight alkaloids identified in hemlock, two are in highest concentrations and account for the toxicity of the plant. These two compounds are g-coniceine and coniine with coniine being about 8 times more toxic than coniceine. Coniine, also called 2-propyl piperidine, is also one of the simplest alkaloids and one of the most toxic, with a dose of less than 0.2 grams being toxic. Pure coniine is a colorless, oily liquid with a bitter taste and unpleasant odor. Other alkaloids that have been identified in hemlock are methyl coniine, ethyl piperidine and pseudoconhydrine.
As a medicine, hemlock has sedative and antispasmodic properties but was used by Greek and Arab physicians for a variety of maladies including joint pain. Obviously it was used with extreme caution since even small amounts could cause untoward affects. This has made its use in medicine rather spotty since the amount needed to migrate from a therapeutic to a toxic dose is very small. An overdose can produce paralysis with toxic doses first causing loss of speech followed by depression of respiratory function and eventual death. At Phaedo 117e, Plato describes the death of Socrates in terms consistent with the action of hemlock:
Socrates walked about, and presently, saying that his legs were heavy, lay down on his back – that was what the man recommended. The man – he was the same one who had administered the poison – kept his hand upon Socrates, and after a little while examined his feet and legs, then pinched his foot hard and asked if he felt it. Socrates said no. Then he did the same to his legs, and moving gradually upward in this way let s see that he was getting cold and numb. Presently he felt him again and said that when it reached the heart, Socrates would be gone.
This essay has provided a historical and botanical perspective, an introduction into the active components of hemlock and finally a brief discussion of its mechanism of action.