Vaping product samples from Wisconsin linked to a rash of serious lung injuries tested by U.S. health regulators showed that more than half contained THC, the psychoactive ingredient in marijuana, according to a summary of a preliminary report seen by Reuters.

Of the THC-containing products, two-thirds also tested positive for Vitamin E acetate, a cutting agent believed to have been used to stretch the amount of THC oil, according to a summary of the report. The Vitamin E additive has been an early focus of investigators seeking to determine the cause of the nationwide outbreak.

Wisconsin is the first U.S. state to disclose results from the U.S. Food and Drug Administration on its testing of samples collected in a public health crisis that has led to nearly 1,300 cases of a mysterious lung injury associated with vaping.

Wisconsin officials submitted 24 vaping products collected from patients with vaping-related lung injuries. All products tested were vaping liquids that were used by people with confirmed or probable cases within three months of developing symptoms. No vaping devices were tested.

Among the results, 14 products contained THC and seven contained nicotine. Of the THC products, nine tested positive for vitamin E acetate. The preliminary summary did not address the other three products tested.

A spokeswoman for the Wisconsin Department of Health Services said it is still not known whether vitamin E acetate is responsible for the injuries.

Some of the samples underwent more extensive testing, and no excessive levels of toxins were detected, she said in an email.

On Friday, FDA officials said it found Vitamin E acetate in 47% of the first 225 products that have been analyzed.

Both the FDA and the U.S. Centers for Disease Control and Prevention have said more than one substance may be behind the outbreak.