The Centers for Disease Control and Prevention this week released new information on its investigation into illnesses and deaths tied to vaping.

The CDC said that of about 500 people who experienced an illness linked to vaping, about 77% reported having used products containing THC, the main psychoactive compound in cannabis.

"The latest findings from the investigation into lung injuries associated with e-cigarette use, or vaping, suggest products containing THC play a role in the outbreak," the CDC said.

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The Centers for Disease Control and Prevention is zeroing in on the role of vapes containing THC as it investigates a spate of illnesses and deaths linked to vaping.

Across the US, at least 805 people have become ill and at least 12 have died from a mysterious lung illness, the CDC said this week. The agency said that it still didn't know for sure what's causing the outbreak and that it wasn't focused solely on products containing THC, the main psychoactive compound in cannabis.

It said that of about 500 people who experienced an illness linked to vaping, about 77% reported having used vapes containing THC, and about 16% said they had used only e-cigarettes containing nicotine.

"The latest findings from the investigation into lung injuries associated with e-cigarette use, or vaping, suggest products containing THC play a role in the outbreak," the CDC said.

The agency reiterated its warning that people should stop buying vaping and e-cig products with THC and nicotine, as it could not rule out nicotine-containing devices as a cause of these illnesses.

Read more: Officials have confirmed 12 deaths and 805 cases of serious lung disease tied to vaping. Here are all the health risks you should know about.

The CDC said it was still not clear whether any single product, substance, or brand was linked to the outbreak of illnesses. There's enormous variety when it comes to vaping devices, ingredients, and brands, making it difficult for investigators to pinpoint a cause.

"We do not know yet what exactly is making people sick," Dr. Anne Schuchat, the principal deputy director of the CDC, said on a conference call on Friday.

She said the agency hadn't determined "whether particular solvents or adulterants are leading to lung injury, or whether cases stem from a single supplier or multiple ones."

Because cannabis is illegal in much of the US, vapes containing THC are largely unregulated. The CDC said most of the THC-containing products that had been tied to the illnesses were obtained from "informal sources," such as people's friends or from a dealer.

The US Food and Drug Administration has been testing samples of cannabis vaping products linked to the illnesses. Some reports have suggested that vitamin E acetate found in some of the products may play a role.

A recent study of 18 THC-containing vape cartridges commissioned by NBC News found that 13 out of the 15 cartridges obtained from the illicit market contained vitamin E and that 10 contained myclobutanil, a fungicide that can turn into hydrogen cyanide when heated.

Read more: Black-market marijuana vapes containing substances like alcohol and caffeine may be to blame for a spate of mysterious lung illnesses

Because vaping is a relatively new practice, there's still a lot we don't know about its health effects, particularly over the long term, Business Insider's Erin Brodwin reported. Recently discovered health risks range from a heightened exposure to toxic metals to a potentially higher risk of a heart attack.