Havana Syndrome describes a real set of symptoms experienced by U.S. government personnel, but the most comprehensive scientific investigations to date have found no evidence of brain injury or a weapon behind it. As many as 334 Americans have qualified for medical care related to these symptoms, reported across more than a dozen countries. The question of whether something physically attacked these people, or whether the explanation is more complex, has divided scientists, intelligence agencies, and the affected individuals themselves.
What People Actually Experience
The symptoms are not in dispute. Starting in 2016, U.S. diplomats and intelligence officers in Havana, Cuba, began reporting a sudden onset of intense head pressure, dizziness, ear pain, and cognitive difficulties. Many described hearing a piercing or buzzing sound just before symptoms began. The episodes were acute, sometimes waking people from sleep, and in some cases led to lasting problems with balance, concentration, and fatigue.
Reports spread well beyond Cuba. Cases surfaced in China, Austria, Colombia, Georgia, Germany, India, Poland, Russia, Vietnam, and even within the continental United States. The U.S. government began formally classifying these events as “anomalous health incidents,” or AHIs, and the pattern drew intense media coverage, congressional hearings, and multiple federal investigations.
What Brain Scans and Blood Tests Show
The largest and most rigorous medical investigation came from the National Institutes of Health, which compared affected personnel to matched controls using advanced MRI imaging and extensive clinical testing. Participants were scanned an average of 80 days after symptom onset, with some scanned as early as 14 days. The results were striking for what they did not find: no consistent brain abnormalities that could distinguish affected individuals from healthy controls. Blood biomarkers and most clinical measures also showed no significant differences.
Where the two groups did differ was in self-reported symptoms. Affected personnel reported significantly more fatigue, post-traumatic stress, and depression than controls. And 41 percent of the affected group, drawn from nearly every geographic area where incidents were reported, met the diagnostic criteria for functional neurological disorders. Most of those individuals specifically met criteria for persistent postural-perceptual dizziness, a condition in which the brain’s balance-processing system becomes chronically disrupted without any structural damage to the brain itself.
This finding is important to understand correctly. Functional neurological disorders produce real, measurable symptoms. They are not “faking it.” The brain genuinely malfunctions, but the cause is not a lesion, a toxin, or a blast wave. It is an abnormality in how the brain processes signals, often triggered or worsened by stress, trauma, or heightened threat perception.
What Intelligence Agencies Concluded
The U.S. intelligence community released assessments in 2023 and updated them in December 2024. Five of seven intelligence agencies assessed it is “very unlikely” that a foreign adversary caused any of the reported incidents. One agency called it “unlikely,” and one abstained. Their reasoning: intelligence collection and investigations have not linked any foreign actor to any reported incident, and newer reports continue to point away from adversary involvement.
All agencies acknowledged they cannot completely rule out the possibility that a small number of incidents involved a foreign actor, simply because investigators could not examine every location where an AHI was reported. But even those leaving the door open suggested the most plausible scenario would involve something based on well-established technology, like an acoustic device or a chemical irritant used for harassment, rather than a novel directed-energy weapon.
Two agencies dissented from the majority view, assessing there was some chance a foreign actor developed a novel weapon or prototype device. This disagreement has kept the political debate alive. In early 2025, congressional committees continued investigating, including reports that the Department of Homeland Security had acquired a device potentially related to AHIs during the Biden administration.
The Microwave Weapon Theory
The most prominent theory holds that pulsed microwave energy could damage brain tissue. A 2020 National Academies of Sciences report examined multiple hypotheses but concluded that no hypothesis had been proven and evidence was lacking. Researchers have proposed theoretical mechanisms by which pulsed microwaves could convert electromagnetic energy into acoustic pressure waves inside the skull. Soviet-era experiments found that animal brains were more sensitive to pulsed microwaves than continuous ones, and that the damage did not appear to come from heating (brain temperatures rose less than half a degree).
The theory is physically plausible in laboratory conditions. Pulsed microwave energy can, at sufficient power levels, create the sensation of sound inside the head, a phenomenon known since the 1960s. Some researchers have proposed it could also disrupt the barrier between blood vessels and brain tissue or cause DNA damage. But no investigation has identified a device, detected microwave emissions at any incident site, or produced the specific pattern of brain injury this mechanism would predict. The NIH imaging studies, which would be expected to reveal structural damage from such an attack, found none.
The Role of Stress and Social Contagion
Experts in mass psychogenic illness have drawn parallels between Havana Syndrome and historical episodes like “shellshock,” where real symptoms spread through a group under extreme stress. The mechanism is social contagion: the spontaneous spread of symptoms, emotions, or behaviors through a network of people who share a common environment or threat perception. Some researchers have noted that new cases appeared after affected personnel were treated at clinics specializing in these complaints, suggesting that awareness of the syndrome may have contributed to its spread.
This does not mean the symptoms are imaginary. Diplomats and intelligence officers working in hostile environments operate under genuine, chronic stress. When a colleague reports a mysterious attack, the heightened vigilance that follows can prime the nervous system to interpret ordinary sensations (a headache, a ringing ear, a moment of dizziness) as evidence of the same attack. Over time, this can trigger the kind of functional neurological disruption that the NIH study documented in 41 percent of cases.
Compensation and Care
Congress passed the HAVANA Act in 2021, creating a framework for financial compensation. The law covers current and former State Department and Commerce Department employees, along with their dependents, for injuries occurring on or after January 1, 2016. To qualify, individuals must demonstrate a qualifying brain injury, which the law defines as either an acute brain injury confirmed by imaging or EEG, a traumatic brain injury diagnosis requiring at least 12 months of active treatment, or the acute onset of persistent disabling neurological symptoms confirmed by testing and requiring at least 12 months of treatment.
The compensation criteria create a practical tension. The law requires imaging or test confirmation of brain injury, but the NIH’s large-scale study found no consistent imaging abnormalities in affected personnel. This means many people with genuine, debilitating symptoms may struggle to meet the standard for payment. A Government Accountability Office review flagged exactly this concern, noting that Americans affected by these symptoms may have difficulty accessing care and compensation.
Where the Evidence Stands
The symptoms are real. The suffering is real. What the evidence does not support is the narrative of a secret weapon systematically targeting American personnel abroad. The most thorough medical study found no brain damage. The intelligence community’s majority view is that foreign adversary involvement is very unlikely. The pattern of symptoms aligns closely with functional neurological disorders triggered by stress and amplified by awareness of the syndrome itself.
None of this is fully settled. A minority of intelligence agencies leave room for a small number of incidents involving a foreign actor, and congressional investigations continue. But the gap between the public perception of Havana Syndrome as a proven directed-energy attack and what the scientific and intelligence evidence actually shows is wide. The people affected deserve care and support. The explanation, based on the best available evidence, appears to be more about how the brain responds to threat and stress than about a hidden weapon.