Havana Syndrome is the informal name for a set of unexplained neurological symptoms first reported by U.S. and Canadian diplomats stationed in Havana, Cuba, in late 2016. Those affected described hearing strange loud sounds or feeling sudden pressure in the head, followed by headaches, dizziness, and insomnia. The phenomenon has since been reported in at least a dozen countries, and despite years of investigation, its cause remains one of the most contested questions in modern intelligence and medicine.
How It Started
The first cases emerged among several dozen personnel attached to the U.S. embassy in Havana. Affected staff described a bizarre experience: an abrupt onset of sound or pressure, sometimes felt on only one side of the head or in a single ear, often with a strong sense that the sensation came from a specific direction. Within moments, many developed vertigo, loss of balance, and ear pain. The episodes were brief, but the symptoms that followed persisted for weeks or months.
Cases soon appeared far beyond Cuba. U.S. government employees and their families reported similar incidents in China, Russia, Austria, Germany, Colombia, India, Poland, Vietnam, Georgia, and even inside the continental United States. As many as 334 Americans with relevant symptoms qualified for care through the military health system, though the true number of affected individuals remains uncertain.
What the Symptoms Look Like
The hallmark of Havana Syndrome is how suddenly it begins. People describe an acute onset of unusual sounds or head pressure, followed almost immediately by a cluster of neurological symptoms. In a clinical study of 86 affected individuals, headache was the most common lingering symptom, reported by 74% of those evaluated. Cognitive difficulties like trouble concentrating or problems with memory followed at 69%. Sleep disorders affected 59%, ringing in the ears (tinnitus) 56%, and balance problems 52%. About a third reported dizziness or changes in vision.
Balance issues are particularly notable. Affected individuals scored significantly worse on standardized balance assessments compared to healthy controls, both on self-reported questionnaires and during clinician-observed walking tests. Roughly 28% of those evaluated were diagnosed with a functional neurological disorder, a condition where the nervous system processes sensory input abnormally even without detectable structural damage.
What Investigators Think Caused It
Several theories have been proposed, and none has been definitively proven.
The leading technical hypothesis involves directed radiofrequency energy, sometimes called pulsed microwaves. A 2020 report from the National Academies of Sciences concluded this was the most plausible explanation among known technologies. More recent research has refined the idea: a single extremely high-power microwave pulse could theoretically damage brain tissue, but the power levels required would be too high to deliver from a distance. A more feasible scenario involves repetitive, very short pulses at lower power densities, which are achievable from distant high-power microwave sources already used in military and other applications. These pulse trains could generate mechanical forces inside the brain without producing noticeable heat.
A second theory centers on mass psychogenic illness, sometimes called mass hysteria. Proponents point to the stressful political and security environment surrounding diplomatic missions, the lack of clear structural injuries on brain scans, and the pattern of cases spreading after initial reports gained media attention. Social connections and exposure to developing cases, even through word of mouth or news coverage, are known to sustain episodes of mass psychogenic illness. However, experts have cautioned that this explanation cannot simply be assumed from the absence of other causes. It needs its own supporting evidence.
A third, less prominent theory involves pesticide exposure. Embassy buildings in Havana were treated with insecticides, and some researchers explored whether organophosphate or pyrethroid chemicals might have played a role. Investigators found that acute pesticide poisoning did not match the symptom pattern. But they could not fully rule out the possibility that chronic, low-level pesticide exposure made some individuals more susceptible to whatever triggered their symptoms, or contributed to variation in how severely different people were affected.
What Brain Scans Actually Show
One of the most significant developments came from a large NIH study published in 2024. Using advanced MRI techniques and extensive clinical testing, researchers found no consistent evidence of detectable brain injury in people reporting Havana Syndrome symptoms. There were no meaningful differences between affected individuals and matched control subjects on most clinical measures, blood biomarkers, or brain imaging. The exceptions were self-reported measures, where affected individuals described significantly worse symptoms, particularly around balance, cognition, and daily functioning.
This finding is important because it does not mean people are faking. The symptoms are real and often debilitating. What it does suggest is that whatever is happening in the brain is not leaving the kind of structural damage visible on current imaging technology, which makes identifying a cause even harder.
What U.S. Intelligence Agencies Concluded
The U.S. Intelligence Community has conducted multiple assessments, most recently updated in December 2024. The conclusion from most agencies is that it is “very unlikely” a foreign adversary is responsible. Five of seven intelligence components reached this judgment, one assessed it as merely “unlikely,” and one abstained. Their reasoning rests on sensitive intelligence reporting that points away from foreign involvement, investigations of key individual incidents, and a review of foreign weapons research that turned up no evidence of a novel device being developed or deployed.
This assessment has been controversial. Some affected personnel and members of Congress have pushed back, arguing that the intelligence review was incomplete or that agencies were too quick to dismiss the possibility of an attack. The debate remains politically charged.
How Affected People Are Treated
There is no specific treatment for Havana Syndrome. Current Department of Defense clinical guidance calls for a symptom-driven approach, meaning each person’s care is tailored to whichever symptoms are most disruptive. This typically involves a team of specialists working together.
For balance and dizziness, early referral to physical therapy and audiology is standard. Vestibular rehabilitation, a type of physical therapy focused on retraining the brain’s balance system, is a core part of recovery for many patients. For cognitive difficulties, cognitive rehabilitation services help people rebuild concentration and memory skills. Sleep problems are addressed through education on sleep hygiene and reducing substances like caffeine and alcohol that disrupt sleep. Headaches are often treated with migraine medications, since the headache pattern frequently resembles migraine variants. For vision-related symptoms, patients are advised to take frequent screen breaks, reduce glare, and sometimes use tinted lenses or blue light filters.
Behavioral health support is woven throughout, with options including mindfulness techniques, breathing exercises, and modified work schedules that allow for rest during the day. Specialty centers within the military health system, including the National Intrepid Center of Excellence, offer comprehensive programs combining neurology, audiology, vestibular therapy, and sleep medicine.
Legal Protections for Affected Personnel
In 2021, Congress passed the HAVANA Act, which authorizes financial payments to federal employees and their dependents who suffered qualifying brain injuries on or after January 1, 2016. To qualify, an individual needs a diagnosis from a board-certified neurologist or rehabilitation physician confirming one of three conditions: an acute brain injury with changes visible on imaging or EEG, a traumatic brain injury diagnosis requiring at least 12 months of active treatment, or acute onset of new, persistent, disabling neurological symptoms confirmed by imaging or clinical testing that also required 12 months or more of treatment.
The bar is deliberately high. The injury must have occurred in connection with hostile activity or a designated incident, and it cannot be the result of the individual’s own misconduct. Applicants submit a formal claim form co-signed by a qualifying physician. The law covers employees of the State Department, CIA, and other agencies, along with their family members who were present during relevant postings.