- Water hemlock grows in temperate wet, marshy areas in mainly North America. According to the U. S. Department of Agriculture (USDA), "water hemlock is the most violently toxic plant that grows in North America."
- Water hemlock is sometimes mistaken for parsnips, due to the similar appearance of their white tuberous roots.
- Although water hemlock was rarely used for headache according to traditional use, there is insufficient available evidence in humans or animals to support the use of water hemlock for any indication.