The American Heart Association's first policy statement on electronic cigarettes backs them as a last resort to help smokers quit. The American Cancer Society has no formal policy but quietly took a similar stance in May.
Both groups express great concern about these popular nicotine-vapour products and urge more regulation. They also stress that proven smoking cessation methods should always be tried first.
But if those fail, "it is reasonable to have a conversation" about e-cigarettes, said Dr Elliott Antman, president of the Heart Association, an organisation that fights heart disease through policy advocacy, research funding and other efforts.
The Cancer Society, another group dedicated to medical research and advocacy, said e-cigarettes "may be a reasonable option" for people who could not quit after trying counselling and approved methods.
Neither group recommends e-cigarettes for smoking cessation, and makers of the devices do not market them that way.
E-cigarettes are battery-powered devices that vapourise nicotine. They've been sold in the US since 2007 and now have millions of users worldwide. They contain less toxic substances than traditional cigarettes do, but little is known about their health effects.
Whether they help or hurt anti-smoking efforts is hotly debated.