Can Poison Hemlock Be Deadly?

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Poison hemlock is one of the more romantic and exciting topics in plant toxicology. The plant is not native to North America, but in the 1800s it was introduced from across the Atlantic for its ornamental value. Today, poison hemlock is found across most of North America.
Historically, poison hemlock was used as medicine (to treat muscle spasms and cause sedation as well as being applied to tumors), but it is most famously known as the method of death chosen by Socrates in 399 BCE. People usually do not eat it intentionally, but rather it is often misidentified as something edible.

The scientific name for poison hemlock is Conium maculatum. The stems are smooth, hollow, and bright green in color, and have red or purple spots; macula is the Latin word for "spot". The leaves are segmented like a fern and described as "lacy". Poison hemlock often has a bad smell described as like "mouse urine" or "musty". The naturally occurring poisons, most notably coniine, are in all parts of the plant.

Poison hemlock belongs to the same plant family (Apiaceae) as carrots, parsnips, fennel, and dill. The plants often involved with foraging mistakes are also a part of the Apiaceae family: angelica, cow parsnip, wild parsnip, wild chervil, wild celery, and Queen Anne's lace. It is difficult to properly identify these plants. To complicate matters, at some phases of the life cycle, common characteristics of poison hemlock, such as spotting or bad smell, might not be present. Concentrations of the poisonous components will vary among plants and are affected by growing conditions. Foraging for edible plants can be fun and rewarding but it can also be dangerous. If you are interested in foraging, join an experienced local group or obtain a field guide with clear pictures and descriptions.

Poison hemlock is a persistent plant that can produce more than 35,000 seeds that can be easily spread by water and animals. The seeds are stable for 3-6 years waiting for the right conditions to sprout and start growing. There are countless cases of animal deaths due to hemlock poisonings because of the plant's rapid growth and intermixing into pastures. The impact on the livestock industry is substantial, and farmers know that poison hemlock must be removed immediately.

If you find poison hemlock in your yard, remove it quickly to keep it from spreading. Wear gloves and pull up the entire plant, including the roots. Your local Office of Agriculture might be willing to help you remove poison hemlock.

The toxicity of coniine has been well documented in livestock, and exposure to the plant is more dangerous for cows than other animals. Initially, there is an excitatory phase with nervousness, tremors, and difficulty walking. Major toxicity and death occur when a depression phase develops. The heart and the diaphragm muscles can slow down more and more, causing death. In humans, coniine affects the nervous system and causes tremors, paralysis, and breathing difficulties. Muscle damage and kidney failure may occur in severe cases. A person with poison hemlock toxicity can usually be successfully treated in a hospital. However, severe symptoms can develop quickly, so it is not safe to try to treat a poison hemlock exposure at home.

Pela Soto, PharmD, BSHS, BS
Certified Specialist in Poison Information