A NIDA (National Institute on Drug Abuse) blog:

In 2016, the U.S. Food and Drug Administration (FDA) established a rule for e-cigarettes and their liquid solutions. Because e-cigarettes contain nicotine derived from tobacco, they are now subject to government regulation as tobacco products. In December 2019, the federal government raised the legal minimum age of sale of tobacco products from 18 to 21. In January 2020, the FDA issued a policy on the sale of flavored vaping cartridges.

While the Centers for Disease Control and Prevention (CDC) and the FDA continue to investigate other possible substances contributing to vaping-related illness and deaths, CDC has identified a thickening agent—Vitamin E acetate—as a chemical of concern among people with e-cigarette or vaping associated lung injuries. 

They recommend that people should not use any product containing Vitamin E acetate, or any vaping products containing THC, particularly from informal sources like friends, family, or in-person and online dealers. They also warn against modifying (changing) any products purchased in stores, or using any vaping products bought on the street. The FDA is asking people, including health professionals, to report any adverse effects of vaping products. The CDC has posted an information page for consumers.

In the past few months, thousands of people have developed serious lung illnesses after vaping (using e-cigarettes). Some people have died as a result.  

As of February 4, 2020:

2,578 cases of these illnesses have been reported to the Centers for Disease Control and Prevention (CDC). The cases were reported by all 50 states, the District of Columbia, and two U.S. territories (Puerto Rico and the U.S. Virgin Islands).

The illnesses have led to 64 deaths in 28 states and the District of Columbia.

The CDC, the U.S. Food and Drug Administration (FDA), and other organizations are investigating the connections between vaping and these illnesses and deaths. In the meantime, the FDA has issued these warnings:

Don’t use any vaping products of any kind bought online, on the street, or from family and friends.

Don’t modify (change) any vaping products purchased in stores, and don’t use THC oil.

The CDC recommends:

Don’t use any e-cigarette (vaping) products—particularly products that contain THC.

Don’t add vitamin E acetate to any vaping products.

Don’t add any other substances not intended by the manufacturer to products.

Vaping is already risky for teens. Tell your friends about the risks, and about the illnesses and deaths associated with vaping. As more facts come in, we’ll report them here.  https://teens.drugabuse.gov/