The National Institutes of Health halted research on "Havana syndrome" Aug. 30 after an internal probe found some patients with the mysterious illness may have been coerced into participating, the Miami Herald reported.
NIH's internal review board found informed consent policies "were not met due to coercion, although not on the part of NIH researchers," a spokesperson told the Miami Herald.
In April, the review board launched a probe into allegations made by some patients with Havana syndrome that the CIA required them to participate in the research as a prerequisite for receiving healthcare, according to CNN. The CIA has denied such claims.
The intelligence agency did not respond to CNN's request for comments on the halted research, though a CIA official told the publication that it takes "any claim of coercion, or perceived coercion, extremely seriously and fully cooperated with NIH's review of this matter, and have offered access to any information requested."
"We greatly value the efforts of the scientific community to better understand these reported health incidents," the official said. "CIA remains committed to ensuring continued access to care for affected officers and to fully investigating any reports of health incidents."
At least 1,5000 U.S. diplomats and intelligence officers have reported symptoms potentially linked to Havana syndrome since the mysterious illness was first identified in 2016, according to CNN.
In March, the NIH published early results from its research, which showed no significant evidence of brain injury among participants. At the time, researchers called the findings a positive development but noted they don't discount many patients' debilitating symptoms.