Concomitant use of electronic nicotine delivery systems (ENDS) and smoked tobacco is associated with an increased risk of incident respiratory symptoms compared with use of either ENDS or smoked tobacco alone, study results published in the American Journal of Respiratory and Critical Care Medicine suggest.

Researchers analyzed data from the Population Assessment of Tobacco and Health (PATH) Study. Specifically, they focused on PATH participants aged 12 years and older who reported no 12-month respiratory symptoms prior to wave 3 (between 2015 and 2016) of the longitudinal study.

Respiratory symptoms were defined as self-reported wheezing or whistling in the chest or nighttime dry cough. Participants were classified by self-reported current ENDS users (n=490), current users of smoking tobacco (n=4061), dual users of ENDS and smoked tobacco (n=900), and “noncurrent users” (n=15,431). The primary outcome was the rate of incident respiratory symptoms, defined by self-reported respiratory symptoms during wave 3 (2016-2018; target 1 year after wave 3 survey).

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Approximately 10.7% of noncurrent users reported incident respiratory symptoms at wave 4. Among exclusive ENDS users, 11.8% reported incident respiratory symptoms by the fourth wave (adjusted odds ratio [OR] vs noncurrent users, 1.17; 95% CI, 0.79-1.74) while 17.1% of exclusive tobacco smokers reported incident respiratory systems (adjusted OR vs noncurrent users, 1.78; 95% CI, 1.56-2.03). Among dual users, 19.7% (adjusted OR vs noncurrent users, 2.22; 95% CI, 1.79-2.75) reported incident respiratory symptoms by the fourth wave.

Participants who were dual users of both products had significantly higher odds of incident respiratory symptoms compared with exclusive tobacco smokers (adjusted OR, 1.24; 95% CI, 1.00-1.55) and exclusive ENDS users (adjusted OR, 1.90; 95% CI, 1.23-2.93).

In a sensitivity analysis that included frequency of use, everyday use was significantly associated with incident respiratory symptoms compared with some-day tobacco smoking (adjusted OR, 1.81; 95% CI, 1.46-2.26). The odds of incident respiratory symptoms remained significantly higher for dual users vs exclusive tobacco smokers (adjusted OR, 1.34; 95% CI, 1.03-1.74).

Limitations of this analysis were the reliance on self-reported survey data and the lack of detailed past ENDS and tobacco usage patterns.

The investigators wrote that “those who use ENDS to stop smoking tobacco should be cautioned against dual use,” recommending “Food and Drug Administration-approved treatments such as varenicline” as an approach to tobacco dependence.


Reddy KP, Schwamm E, Kalkhoran S, Noubary F, Walensky RP, Rigotti NA. Respiratory symptom incidence among people using electronic cigarettes, combustible tobacco, or both. Am J Respir Crit Care Med. Published online April 15, 2021. doi:10.1164/rccm.202012-4441LE