As the market for brain stimulation devices and apps grows, a University of Pennsylvania instructor and a Canadian neuroethicist are calling for more oversight of the largely unproven technology.

In an essay in Thursday’s issue of the journal Science, the two argue that consumers want and need better information about direct-to-consumer neurotechnology products, a market that is expected to exceed $3 billion in sales by 2020. The category includes devices that purport to monitor brain activity or provide low levels of electrical stimulation to the brain through transcranial direct current stimulation (tDCS) with the goal of improving cognitive or athletic performance and mental health. It also includes games and apps that claim to sharpen thinking or monitor mental health.

“This is an area that’s increasing that we really need to pay attention to,” said Anna Wexler, an instructor in the department of medical ethics and health policy at Penn.

These products are often marketed as science-based, but Wexler and Peter B. Reiner, a neuroethicist at the University of British Columbia, wrote that “one overarching issue is whether direct-to-consumer neurotechnologies work as advertised.”

They said many companies have done little research on the effectiveness of their products. Other devices are “loosely based” on laboratory science that may not be applicable to a home setting. For example, products that monitor brain activity with electroencephalography (EEG) use fewer electrodes than those in the lab and the electrodes must be placed by untrained consumers. Scientists themselves are still debating about the effectiveness of many of the approaches currently being pushed directly to consumers.

“It’s not like a settled thing,” said Wexler, who has been studying neurotechnology products and home users for several years. In a study published last year, she found that consumers used the devices more often than recommended. A typical respondent to her survey of people who had bought the products was a wealthy, well-educated, liberal man in his 40s. About a third were using the devices to self-treat depression.

Neurostimulation is a hot research topic, and the field shows considerable promise, but 39 researchers signed an open letter to the DIY transcranial direct current stimulation community in Annals of Neurology in 2016 outlining their concerns about doing at-home brain stimulation outside of scientific research.

While the most obvious safety concern of the devices is occasional burns to the skin, the letter pointed out that researchers do not yet know enough about the long-term and unexpected results of brain stimulation. Because many parts of the brain work in concert, electrical stimulation directed at one part affects more of the brain than many users realize. Different people are affected in different, sometimes contradictory, ways. While the stimulation may cause one part of the brain to work more efficiently, another may work more slowly. It is not yet known how long both the positive and negative effects of stimulation last.

“We just don’t know what the long-term effects of brain stimulation are,” said Wexler, who did not sign the letter.

While there is some evidence that brain training games can improve functioning in a particular cognitive domain, say, attention, whether they have broader impact that translates into better everyday functioning remains controversial.

Wexler said that devices that claim to monitor mood could have the unintended effect of increasing stress if their reports were inaccurate.

The brain stimulation and EEG devices come in multiple shapes. Some look like futuristic headsets or headphones. Some have electrodes the consumer has to attach. They’re sold at a wide range of price points, with several from $150 to $300.

From a regulatory standpoint, neurotechnologies have much in common with dietary supplements, a category that Wexler says is “far more dangerous.” Supplements largely escape being regulated as drugs by not claiming to treat specific diseases. Neurotechnologies have so far avoided regulation by the Food and Drug Administration, Wexler and Reiner said, by “limiting their claims to wellness” rather than saying they help specific medical problems.

Wexler said consumers need better information to make informed decisions. Evaluating each individual product would be difficult because there are frequent tweaks to physical design and software. She proposes a working group made up of scientists, consumers, ethicists, regulators, and industry representatives to write “succinct” appraisals of what science supports and where the gaps in knowledge lie.