The tea leaves bought at Sun Wing Wo Trading Company contained the plant-based toxin Aconite, the Department of Public Health said Friday.
A man in his 50s last month and a woman in her 30s this month became critically ill within an hour of drinking the tea, and both remain hospitalized, health officials said.
Each person grew weak then had life-threatening abnormal heart rhythms that required resuscitation and intensive care.
Aconite, also known as monkshood, helmet flower and wolfsbane, is used in Asian herbal medicines. But it must be processed properly to be safe.
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Health officials are working to find the original source of the tea leaves, and they are warning others to stop consuming it.
“Anyone who has purchased tea from this location should not consume it and should throw it away immediately,” said Dr. Tomas Aragon, health officer for the city and county of San Francisco.
“Aconite poisoning attacks the heart and can be lethal.”