All parts of the Hemlock plant are highly toxic and are poisonous to all mammals and other animals that eat it. Even touching the plant can cause symptoms.
The seeds and roots are more toxic than the leaves and the whole plant becomes most poisonous in the spring when the concentration of toxins is at its peak.
Ingesting around six to eight hemlock leaves can be fatal for adult humans. The symptoms begin around 30 minutes after ingesting with a narcotic-like effect, making the victim sleep or lose consciousness, trembling, dilation of pupils, weak pulse, convulsions and coma. Muscular paralysis leading to paralysis of the respiratory muscles causes death from oxygen deprivation. Artificial ventilation can be used to keep the victim alive until the effects have worn off 48–72 hours later.