Using e-cigarettes containing liquids with high percentages of alcohol can impact users’ psychomotor skills, according to a new study from the Yale School of Medicine.

The study targeted alcohol levels in e-cigarettes, whose liquid substances include variable levels of alcohol because they are not regulated by the Food and Drug Administration. Even though many nicotine liquids do not contain alcohol, or contain only trace amounts of alcohol, the lack of labeling makes it difficult for users to obtain compete and accurate information about products, according to researchers.

In the study, which is the first to systematically study the effects of inhaled alcohol from e-cigarettes, researchers tested 16 participants’ feelings of intoxication, psychomotor skills and levels of nicotine and alcohol after they inhaled one of two different nicotine mixtures from the same e-cigarette. One mixture was 0.4 percent alcohol, while the other was 23.5 percent alcohol. Study participants took the same dexterity test multiple times, and users that inhaled the first mixture slightly improved their performances on the test, while users that inhaled the second, higher-alcohol vapor did not demonstrate the same improvements. However, the groups did not report any difference in subjective feelings of intoxication.

Their finding, that higher-alcohol e-cigarette liquids negatively impact users’ psychomotor skills, is an important piece of a complex puzzle, study authors said.

“There are many different types of concerns regarding the use of e-cigarettes, specifically regarding ingredients that are in e-liquids and the effects of these added chemicals on health,” study co-author and medical school clinician Gerald Valentine said. He noted that alcohol was one such unlabeled ingredient in some e-cigarette liquids.

According to study co-author and medical school professor emeritus Peter Jatlow, three subjects in the higher-alcohol group tested positive for the alcohol metabolite ethyl glucuronide, which verified that those subjects had absorbed alcohol along with the nicotine.

The study’s findings may have varied implications for different users. For example, psychomotor impairment is not a concern for people smoking most conventional, drugstore e-cigarettes such as Blu, Valentine said. However, he noted that the findings may be very relevant to certain subgroups, such as vaping enthusiasts who mix their own nicotine liquids from online recipes.

Many forms of e-cigarettes may be beneficial for certain users, such as those who are trying to quit smoking, Valentine said. According to School of Medicine professor Mehmet Sofuoglu, another study co-author, the available evidence from short-term studies suggests that e-cigarettes are less harmful than traditional tobacco cigarettes.

“Given the widespread and unregulated use of e-cigarettes, especially by youth and other vulnerable populations, further studies are needed to evaluate both the acute safety and long-term health risks of using alcohol-containing e-cigarettes,” Sofuoglu said.

Future studies will likely come out of this research, Valentine said. Potential further directions include research about the threshold of impairment, long-term effects and the potential reinforcing properties of inhaling nicotine and alcohol simultaneously.

By 2014, roughly 12 percent of American adults had tried e-cigarettes at least once, according to a study conducted by the Centers for Disease Control and Prevention.