For the first time, the Centers for Disease Control and Prevention (CDC) said it suspects vaping THC—a compound in marijuana—is tied to the hundreds of lung illnesses and at least 12 deaths that have been reported across the country.

During a press briefing on Friday, CDC officials said the latest findings of their investigation “suggest THC products play a role in the outbreak.” Previously, the CDC reported that many of the sick people reported using THC in their vape pens, but officials stopped short of tying the illnesses to the drug.

In data collected from more than 500 patients, 77% reported using THC products or using both THC and nicotine. About 36% reported using only products with THC. The CDC said 16% of patients said they only vaped nicotine and not THC.

This information is based on self-reports from patients.

Officials in Illinois and Wisconsin said that “Dank Vapes” was the most common used brand of THC-filled cartridges in their states. “Dank Vapes” is a very popular brand and easily obtainable, according to officials. The CDC interviewed 86 patients who had lung-related issues tied to e-cigarettes in the two states. Around 70% of those patients said they used “Dank Vapes,” according to the CDC.

The CDC also said “Dank Vapes” appears to be the leader in a large class of counterfeit brands of vape cartridges with THC that have similar packaging and are easy to buy online and in stores.

Others labels include TKO, Off White, Moon Rocks, Cookies, Chronic Carts, Mario Carts, Kingpen, California Confidential, Cereal Carts and Supreme G.

“We are in the midst of a complex investigation that spans nearly all states and involves serious life-threatening disease in young people,” Dr. Anne Schuchat, the Principal Deputy Director of the CDC said at the briefing.

There are 805 confirmed and probable cases of lung injury tied to vaping, according to the CDC. The CDC has also reported 12 deaths tied to vaping, but it expects that number to rise as state and local officials report these kind of deaths to the CDC. The Associated Press counted 13 vaping deaths so far.

“Sadly I do believe there are additional ones [deaths],” Schuchat said.

Though the CDC has found a pattern with THC, officials said they are still unable to say what exactly is making people sick.

“We can unfortunately not identify one product, brand, source or device that is common across all patients,” Dr. Jennifer Layden, Illinois’s Chief Medical Officer and State Epidemiologist said at the briefing.

The CDC continues to suggest that people consider not using e-cigarettes at all, especially ones that contain THC.

Write to Josiah Bates at josiah.bates@time.com.