More than 1,000 patients who took borrage herbal medicine reported a sudden increase in allergic reactions that led to death, according to new data from the U.S. Centers for Disease Control and Prevention.

Borrage is a synthetic extract of a common plant, but the exact chemical structure of the substance is unknown.

The Associated Press identified the patients, some of whom are in their 60s or 70s, as the first cases in a series of cases that the CDC said could be linked to the drug.

A federal study released earlier this year found that about 10,100 people had died from reactions that appeared to be related to borra.

More than 6,700 of those people had taken borragics and about 1,300 died from it.

The CDC said it has tested more than 5,000 samples from the drug, and more than 2,000 have tested positive for coronavirus.

Some of those cases occurred in states that banned or limited use of borragics, which has not been linked to any fatalities.CDC officials say it is too early to say whether any deaths have been linked specifically to borragics.

The AP has reached out to the CDC for comment.

The Centers for Medicare and Medicaid Services, which administers boragra, said in a statement that it is “reviewing the reports and will provide additional information as it becomes available.”