Havana Syndrome: What Does the Medical Evidence Actually Show?

Reports of Havana Syndrome—now generally discussed by the US government under the broader category of Directed Energy Bio-Effects (DEBE)—have produced an unusually complicated medical record.

Some affected personnel reported sudden experiences including unusual sounds or pressure sensations, followed in some cases by dizziness, headache, nausea, cognitive difficulties, sleep disturbance and problems with balance. Researchers subsequently investigated whether these reports were accompanied by measurable neurological, vestibular or other physiological abnormalities.

The resulting evidence requires careful interpretation. Some studies reported objective abnormalities or group-level differences, while other investigations found no consistent pattern of structural brain injury or biological marker capable of identifying a distinct syndrome.

This review examines what clinicians and researchers actually observed, how strong those findings are, which results have been disputed or superseded by later evidence, and—crucially—what the medical evidence can and cannot tell us about causation.

Medical findings and causal attribution are separate questions. Evidence that an individual experienced genuine symptoms or measurable abnormalities does not, by itself, establish what produced them.

1. What Symptoms Were Reported?

The reports grouped under Havana Syndrome or Anomalous Health Incidents did not all follow the same clinical pattern. However, some of the most distinctive early accounts described a sudden onset while the individual was in a particular location.

In these cases, the initial experience was sometimes described as an unusual sound, pressure or vibration, occasionally with an apparent direction or sharply defined spatial boundary. Some individuals reported that moving away from the location reduced the sensation.

Acute symptoms reported in association with these events included vertigo, disequilibrium, ear discomfort, headache, nausea and cognitive disruption. Some affected personnel subsequently reported longer-lasting problems involving balance, concentration, memory, sleep and fatigue. 

Importantly, this pattern was not present in every reported case. As awareness of AHIs increased and reports emerged from additional locations, the category became increasingly heterogeneous. Some incidents contained the distinctive acute sensory onset; others did not. Medical histories, circumstances and delays before clinical examination also varied. 

This makes the term Havana Syndrome potentially misleading if it is interpreted as a single, established disease with one cause. The reported symptoms are evidence about what individuals experienced; they do not, by themselves, identify the mechanism responsible.

2. Symptoms vs Objective Medical Findings

A crucial distinction in evaluating Anomalous Health Incidents is the difference between symptoms, clinical signs and biomarkers.

Symptoms are experiences reported by a patient, such as pain, dizziness, ringing in the ears or difficulty concentrating. Clinical signs are findings observed or measured by a clinician. Biomarkers are measurable biological features associated with a condition. These categories can overlap, but they are not interchangeable.

A person can experience genuine and disabling symptoms without having a visible abnormality on routine brain imaging. Conversely, finding a measurable difference in a group of patients does not automatically establish what caused that difference. Appropriate controls, sample sizes, previous health, testing conditions and replication all matter when interpreting such findings. 

Early clinical studies of affected personnel reported neurological, vestibular and cognitive abnormalities, and some imaging studies described differences between affected groups and comparison groups. These investigations were important in documenting the experiences of patients, but they also faced limitations including relatively small samples, varied exposure histories, incomplete baseline information, referral bias and difficulties selecting genuinely comparable controls. 

Later research therefore became particularly important. In 2024, National Institutes of Health teams conducted detailed studies involving affected US government personnel and matched controls. Participants could have severe and persistent symptoms, but the investigators did not find significant group-level evidence of MRI-detectable brain injury or most of the proposed biological abnormalities. Some participants met criteria for persistent postural-perceptual dizziness, a recognised functional vestibular disorder. 

The appropriate interpretation is narrow: the studies did not identify the hypothesised group-level structural or biological signature using the tests employed. They did not establish that participants were healthy, that their symptoms were fabricated, or that every case had the same cause.

3. What Did the Later NIH Research Find?

Later NIH research provided a more detailed picture of people reporting these experiences. The studies found that some participants continued to experience severe and persistent symptoms, including problems involving balance, cognition, sleep and other functions.

At the same time, the researchers did not find significant group-level evidence of MRI-detectable brain injury or most of the biological abnormalities that had previously been proposed. Some participants met criteria for persistent postural-perceptual dizziness (PPPD), a recognised functional vestibular disorder.

These findings need to be interpreted carefully. The absence of a detectable structural brain injury does not mean that a person's symptoms were imaginary, fabricated or unimportant. Conversely, finding a medical condition or measurable difference does not by itself establish what caused it or whether the same mechanism was responsible across all reported cases.

The NIH findings therefore help narrow the medical questions, rather than providing a single explanation for every case.

4. What Did the National Academies Conclude About Possible Mechanisms?

The 2020 National Academies of Sciences, Engineering, and Medicine assessment considered several possible explanations for the distinctive acute features reported in some cases. These included infectious, chemical, psychological or social mechanisms, and directed energy.

Among the mechanisms considered, the committee judged directed pulsed radio-frequency (RF) energy to be the most plausible explanation for certain acute features in a subset of cases. The reasoning included the reported abrupt onset, apparent directionality, location specificity, unusual sounds and the established microwave auditory effect.

However, this was not a conclusion that RF energy caused all reported cases. The assessment did not identify a specific device, operator or country responsible, and it did not establish that directed RF was the cause of the wider collection of symptoms subsequently associated with Havana Syndrome or AHIs.

This distinction is important: a mechanism can be scientifically plausible without being demonstrated as the cause of a particular incident.

5. What Does the Microwave Auditory Effect Tell Us?

The microwave auditory effect provides an important part of the scientific background to these discussions. Research beginning with Allan Frey demonstrated that appropriately pulsed radio-frequency energy can produce auditory sensations such as clicks, buzzing, hissing or knocking without ordinary sound reaching the ear.

Later experiments went further. Work by Sharp and Grove demonstrated the perception of recognisable prerecorded single-syllable digits encoded into pulse sequences. Justesen subsequently reported reception of Morse-code information under experimental conditions.

These experiments establish that pulsed RF energy can produce auditory perception and that information can be encoded into the resulting auditory sensation under defined experimental conditions.

They do not, however, demonstrate that Havana Syndrome or any particular AHI was caused by this mechanism. Nor do they establish that arbitrary continuous speech, or a specific message, was transmitted to an individual in any reported incident. Those are separate questions requiring evidence about the RF exposure, its characteristics, the environment and the individual case.

6. Why a Plausible Mechanism Is Not Proof of Cause

The existence of a plausible physical mechanism is not, by itself, proof that the mechanism caused a particular person's symptoms.

For RF energy to be established as the cause of an individual incident, additional evidence would be needed. This could include evidence that RF energy was actually present, that its characteristics were consistent with the proposed mechanism, that sufficient energy could have reached the person under the relevant conditions, and that the exposure could account for the observed effects.

Other possible explanations also have to be considered. These can include acoustic or environmental factors, medical or vestibular conditions, and psychological or social mechanisms. More than one factor could potentially contribute to an individual's experience.

The microwave auditory effect therefore establishes an important scientific possibility, but it does not by itself establish what caused a particular AHI. Similarly, an unexplained incident is not positive evidence that a directed-energy attack occurred.

Keeping these questions separate is essential when interpreting the medical evidence: what a person experienced, what medical findings demonstrate, what mechanism could produce those effects, and whether a particular actor caused them are different questions.

7. Conclusion

The medical evidence surrounding Havana Syndrome and AHIs does not currently point to one simple explanation for every reported case.

The evidence establishes that people experienced genuine and sometimes persistent symptoms. It also shows that some proposed biological explanations have not been consistently demonstrated at group level, while recognised conditions such as PPPD may account for some of the symptoms experienced by some individuals.

Separately, experimental research establishes that pulsed RF energy can produce auditory sensations and, under defined conditions, can convey encoded information through those sensations. This provides an important scientific mechanism to consider when evaluating reports involving unusual sounds or apparent directionality.

But these findings should not be combined into a conclusion that the RF mechanism caused every AHI, or that a particular incident was the result of deliberate attack. Establishing that would require case-specific evidence.

The most useful approach is therefore to keep the different levels of evidence separate: reported experience, medical findings, established physical mechanisms, and attribution of cause.

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