People living with depression, anxiety or other mental health conditions are twice as likely to have tried e-cigarettes and three times as likely to be current users of these devices as people without mental health disorders, research says.
They are also more susceptible to trying e-cigarettes in the future in the belief that doing so will help them quit, the scientists said.
"Since the safety of e-cigarettes is still unknown, their use by non-smokers could put them at risk," said Sharon Cummins, an assistant professor at University of California's (San Diego) school of medicine.
The study shows that smokers, regardless of their mental health condition, are the primary consumers of the nicotine delivery technology.
People with mental health disorders also appear to be using e-cigarettes for the same reasons as other smokers - to reduce potential harm to their health and to help them break the habit.
"So far, non-smokers with mental health disorders are not picking up e-cigarettes as a gateway to smoking," Cummins noted.
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The study is based on a survey of Americans' smoking history, efforts to quit and their use and perceptions about e-cigarettes.
People were also asked whether they had ever been diagnosed with an anxiety disorder, depression or other mental health condition.
People with mental health conditions have largely been forgotten in the war on smoking.
"But because they are high consumers of cigarettes, they have the most to gain or lose from the e-cigarette phenomenon," the research, published in the journal Tobacco Control, concluded.