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Milkweed Plant Can Cause Serious Poisoning

The Bottom Line

Milkweed grows throughout the US and is essential for the survival of monarch butterflies. All parts of the plant contain toxic cardiac glycosides, which can cause nausea, diarrhea, weakness, and confusion in small amounts, and seizures, heart rhythm changes, respiratory paralysis, and even death in large amounts. Milkweed can also irritate the skin and eyes if touched.

The Full Story

The Asclepias genus is a group of perennial flowering herbs also known as milkweed due to their milky sap. There are over 200 species in the Asclepias genus that are native to Africa, North America, and South America. Monarch butterflies cannot survive without milkweed; their caterpillars only eat milkweed plants, and adult monarchs need milkweed to lay their eggs. The plant is most easily identified by its distinctive pod-like fruit containing densely packed seeds. When the fruit pods mature and turn brown, they burst and release the seeds. All parts of the plant contain toxic cardiac glycosides. The highest concentrations of cardiac glycosides are found in the sap, followed by the stems, leaves, and roots. The plant is most toxic just before it reaches maturity.

Cardiac glycoside-containing plants have been used since ancient times for medical purposes. Milkweed has been used by indigenous peoples for swelling and rashes, diarrhea, and respiratory issues. However, cardiac glycosides have narrow therapeutic windows, meaning small changes in dosage can result in large differences in toxicity. Due to the prevalence of the plant, exposure to milkweed plants is very common. From 2011 through 2015, Poison Control received more than 7,000 calls regarding cardiac glycoside-containing plants.

When swallowed, symptoms of milkweed toxicity usually appear within a few hours. Initial symptoms consist of stomach upset, nausea, vomiting, abdominal pain, diarrhea, weakness, lethargy, and confusion. Severe toxicity includes seizures, heart rhythm changes, and severe slowing of the heart rate. Milkweed can cause coma and respiratory paralysis, which can lead to death.

The sap from the plant can also cause skin and eye irritation. If your skin comes into contact with milkweed sap, you should immediately wash the affected area thoroughly with soap and water. If someone experiences eye irritation after getting sap in their eye, gently rinse the eye with room temperature water for 10–15 minutes. If there are any persistent skin or eye pain or symptoms, seek medical examination and treatment.

If you suspect someone has been exposed to milkweed and is having a problem, check the webPOISONCONTROL® online tool for guidance or call Poison Control at 1-800-222-1222.


For More Information

Butterfly milkweed Asclepias tuberosa L. Washington: US Department of Agriculture; 2006 May 31 [cited 2020 Dec 1].

Taylor D. Plant of the week: common milkweed (Ascepias syriaca L). Washington: US Forest Service [cited 2020 Dec 2].


References

Butterfly milkweed Asclepias tuberosa L. Washington; US Department of Agriculture; 2006 May 31 [cited 2020 Dec 1].

Common milkweed Asclepias syricacia F. asclepidaceae. Fall wildflowers of New England. Waltham (MS): Brandeis University; [cited 2020 Dec 1].

Hack JB. Cardioactive steroids. In: Nelson LS, Howland MA, Lewin NA, Smith SW, Goldfrank L, Hoffman RS, editors. Goldfrank's toxicologic emergencies. 11th ed. New York: McGraw Hill; 2019.

Nelson CJ, Seiber JN, Brower LP. Seasonal and intraplant variation of cardenolide content in the California milkweed, Asclepias eriocarpa, and implications for plant defense. J Chem Ecol. 1981 Nov;7(6):981–1010.

Plants–cardiac glycosides. In: IBM Micromedex POISINDEX System [Internet database]. Greenwood Village (CO): IBM Watson Health; c2020 [cited 2020 Nov 29].

Poisoned?

Call 1-800-222-1222 or

HELP ME online

Prevention Tips

  • Have all your plants (indoor and outdoor) correctly identified by a knowledgeable expert.
  • Keep all plants out of the reach of children and pets.
  • Do not prepare your own herbal medicines.
  • Do not prepare food or tea from plants unless you are an expert and know how to do so safely.

This Really Happened

Case 1. A 46-year-old woman placed cut milkweed into a jar of water. She eventually removed the milkweed from the jar but forgot to dump out the water. She later drank from the jar. She took a dose of Pepto Bismol before calling Poison Control. Her only complaint was a bad taste in her mouth. Poison Control instructed her to drink water to help with the taste. Poison Control followed up with her 3½ hours later, and she did not have any symptoms.

Case 2. A 12-year-old boy ate a piece of a milkweed plant at school. He liked its taste, so he took two more bites. The school's assistant principal called Poison Control about an hour after the ingestion, at which time the boy did not have any symptoms. Poison Control instructed the assistant principal to continue to monitor the boy for symptoms, although severe symptoms were not expected from this small exposure. Poison Control called the school the next day and learned that the boy never developed symptoms.