Are e-cigarettes bad for your health? Could they serve as a gateway to tobacco smoking for young people? Or are they a powerful weapon against traditional tobacco that gives smokers a healthier way to get their nicotine fix?
The best scientists can come up with at this point is: they don't know the answers to any of those questions.
The debate over e-cigarettes is ongoing and heated, even as more cities ban their use in public, as Los Angeles and Long Beach did earlier this month.
The problem is, when it comes to e-cigarettes, there is little conclusive research on their health impacts, on whether they help people quit, or even on what is in them. That dearth of data has made it impossible for public policy makers or researchers to reach consensus on the devices, or on how to regulate them.
"I’d say about the only consensus is that more research is needed," said Dr. Wilson Compton, deputy director of the National Institute on Drug Abuse.
A big part of the reason there is so little good research on e-cigarettes is that the product itself is constantly changing, Compton said.
"Many projects kind of lump e-cigarettes into one category," he said, "and yet the amount of nicotine delivered, the potential for harmful additional components varies considerably from one brand to the next."
In other words, trying to assess whether e-cigarettes help smokers quit is not as easy as simply comparing smokers who use e-cigarettes with smokers who don’t.
Not only do different e-cigarettes have different contents, but the companies making them are frequently experimenting with new recipes, said Dr. Tim McAfee, director of the Centers for Disease Control and Prevention's Office on Smoking and Health.
"The characteristics of what people are using are changing from month to month," McAfee said, noting that the product is evolving too quickly for researchers, including his own, to keep up.
"Our surveillance instruments, where the questions literally were designed a year or two ago, have not caught up with this marketplace evolution," McAfee said.
To catch up, McAfee said scientists will need help from the government. E-cigarette production is unregulated. If Washington sets manufacturing standards, researchers could produce more reliable data because they would have fewer variables to account for when designing their studies, he said.
The Food and Drug Administration has announced that it will begin regulating e-cigarettes, although it has not said when.
The regulatory effort will be informed in part by a large-scale, multi-year study the FDA has launched in concert with the National Institutes of Health. The study, called the Population Assessment of Tobacco and Health, is collecting detailed data about how tens of thousands of people across the US use e-cigarettes and other tobacco products.
The study will fill in much of the current knowledge gap regarding e-cigarette use, said Dr. Cathy Backinger, a research director at the FDA’s Center for Tobacco Products.
"Are kids and adults first trying them, and why are they trying them?" she said. "How old were they when they tried them? What types of e-cigarettes do they have? Are they using them in fact to quit smoking or are they using them to get nicotine when they can’t smoke?"
The study will also collect biological samples from people in an effort to track how e-cigarette-use affects their health and the health of people around them over years. It will also track thousands of non-smokers to see if they start using tobacco products or e-cigarettes, and why.
Researchers are eagerly awaiting the first batch of data, which is expected sometime next year.