Unlike the species in yesterday’s entry, there is ample documentation about the toxicity and danger of species of Veratrum.
From Wikipedia’s entry on Veratrum:
Veratrum species contain highly toxic steroidal alkaloids (e.g. veratridine) that activate sodium ion channels and cause rapid cardiac failure and death if ingested. All parts of the plant are poisonous, with the root and rhizomes being the most poisonous.
Symptoms typically occur between thirty minutes and four hours after ingestion and include nausea and vomiting, abdominal pain, numbness, headache, sweating, muscle weakness, bradycardia, hypotension, cardiac arrhythmia, and seizures. Treatment for poisoning includes gastrointestinal decontamination with activated charcoal followed by supportive care including antiemetics for persistent nausea and vomiting, along with atropine for treatment of bradycardia and fluid replacement and vasopressors for the treatment of hypotension.
In addition to the above, plants in the group also have teratogenic properties, i.e., they disrupt the physiological development of (mammalian) fetuses. Cyclopamine (warning: risky click–deformed calf) is one of these disrupting alkaloids, potentially preventing the fetal brain from dividing into two lobes and causing a single eye (like the mythical Cyclops).
Despite the dangers, traditional medicine practitioners in both North America and Asia have used extremely low doses of Veratrum in their practice. When harvested in the winter, the alkaloids in the roots have partially degraded, lessening the danger of use from “very” to something a bit less. The above-linked Wikipedia entry goes into more detail.