A cluster of unexplained neurological symptoms

The term covers a cluster of sudden neurological-type symptoms reported by diplomats, intelligence officers and military personnel in Cuba, China, Europe, Vietnam and elsewhere. Researchers have proposed several explanations, including directed energy or microwave weapons, environmental or medical causes, and stress or group psychological effects. Large government-backed studies and intelligence reviews have not found evidence of a weapon or of consistent physical injury. Many affected people still report real, disabling symptoms and believe a weapon caused them. Reporting in 2026 about a seized device has renewed debate but has not settled the cause. Evidence is therefore mixed and the picture could change.

• First reported in 2016 by US embassy staff in Havana, Cuba. Some reports suggest cases as early as 2014.
• Symptoms include headache, dizziness, balance problems, ear pain, cognitive trouble, and insomnia. They sometimes last months.
• NIH studies published in March 2024 found no MRI-detectable brain injury or consistent biological abnormality in affected people compared with controls. The authors said this does not rule out an event at the time of the incident.
• The US intelligence community's updated assessment, released in January 2025, judged it very unlikely or unlikely that a foreign actor caused the incidents.
• In January 2026, media reported that the US had obtained and was testing a portable device that emits pulsed radio-frequency energy. Its link to the cases is unconfirmed.

1. Havana syndrome en.wikipedia.org
2. People with ‘Havana Syndrome’ Show No Brain Damage or Medical Illness scientificamerican.com
3. What to know about Havana Syndrome and a device that might be linked to it - CBS News cbsnews.com
4. Pentagon eyes ‘treatments and countermeasures’ as it reshapes AHI cross-functional team defensescoop.com
5. NIH studies find severe symptoms of “Havana Syndrome,” but no evidence of MRI-detectable brain injury or biological abnormalities nih.gov
6. "Havana Syndrome" mystery takes unusual turn. Here's what to know about the illness axios.com
7. What is Havana Syndrome, And Why Is It Making Headlines Again in 2026 - North American Community Hub nchstats.com
8. Havana syndrome: new book and evidence revive questions over Russia role - Brit Brief britbrief.co.uk

The term describes reported health problems rather than a disease with a confirmed cause or a definitive diagnostic test. Researchers have considered several explanations, and different cases may have different causes. The absence of a consistent abnormality on brain scans does not mean the symptoms are imagined, nor does it rule out every possible earlier injury.

• The U.S. government calls these reports “anomalous health incidents,” or AHIs.
• Some people describe a sudden unusual sound, head pressure or ear pain before other symptoms develop.
• Similar incidents have been reported outside Cuba, including in China.
• NIH studies published in March 2024 found no significant group differences in MRI measures of brain structure or function, despite substantial symptoms.
• Directed radiofrequency energy has been proposed as a possible explanation, but proposing a plausible mechanism does not establish that it caused the reported incidents.

1. nih.gov
2. irp.nih.gov
3. dni.gov
4. dni.gov
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6. nibib.nih.gov
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8. nibib.nih.gov

Havana syndrome refers to a cluster of acute and chronic neurological symptoms reported primarily by US diplomats, intelligence officers, and military personnel, beginning in Havana, Cuba, in 2016. Reported symptoms include auditory sensations, ear pain, vertigo, cognitive difficulties, and headaches. While early theories suggested directed-energy weapons or sonic devices, extensive multi-agency investigations and clinical studies by the National Institutes of Health have found no consistent clinical biomarkers, brain damage, or foreign weapon involvement across the reported cases.

• Cases were first reported in late 2016 by US and Canadian embassy staff stationed in Havana, Cuba, who described sudden head pressure, loud sounds, and vertigo.
• Formally termed Anomalous Health Incidents (AHIs) by the US government, similar symptoms were later reported by hundreds of personnel in multiple countries.
• A 2023 US intelligence community assessment concluded it was 'very unlikely' a foreign adversary or directed-energy weapon was responsible.
• A comprehensive 2024 National Institutes of Health study published in JAMA found no significant brain injuries or biological differences in affected personnel compared to healthy controls.
• Alternative hypotheses have ranged from directed pulsed radiofrequency energy to mass psychogenic illness, crickets, and preexisting medical conditions.

This is a 'what is it' question, so the answer is a description rather than a yes or no. The literature agrees on the clinical picture — an acute auditory-vestibular phase and a chronic phase of nonspecific neurological and cognitive symptoms among diplomats and intelligence staff — but not on the cause. Reviews describe the evidence base as thin and the cause as unidentified; US intelligence assessments favour mass psychogenic illness or another unknown mechanism over a hostile weapon, without fully closing the question. Because the underlying cause is genuinely unsettled, the evidence rating is mixed and the answer is open.

• First cases were reported by US embassy personnel in Havana in November 2016, after the embassy had reopened; Canadian diplomats reported similar symptoms.
• Symptoms typically began abruptly with a strange sound or sense of pressure, and included headache, dizziness, tinnitus, visual disturbance and cognitive complaints, sometimes persisting for months.
• The US government now labels the cases 'anomalous health incidents' (AHIs); cases have also been reported in China, Cuba, Vietnam, Austria, Russia and the United States.
• A 2023 Office of the Director of National Intelligence assessment found it 'very unlikely' a foreign adversary was causing the incidents and pointed to mass psychogenic illness as the most plausible explanation, though some agencies dissented or remained undecided.
• Two 2024 NIH studies of more than 80 affected people found no evidence of lasting brain damage or neurodegeneration, though symptoms were genuine; the US began paying compensation under the 2021 HAVANA Act, with payments announced in July 2026.

1. Havana syndrome: US to compensate victims bmj.com
2. Havana syndrome: Overview for otolaryngologists - Skip to main contentSkip to article sciencedirect.com
3. Mystery illness among U.S. diplomats did not cause permanent brain damage - Skip to main content science.org
4. Havana syndrome: a scoping review of the existing literature - The Royal College of Surgeons of England Library Surgical Library rcseng.ovidds.com
5. Chairman Pfluger Opens ‘Havana Syndrome’ Hearing: “It is Paramount That We Acknowledge the Gravity of the Situation” homeland.house.gov
6. COMMITTEE ON HOMELAND SECURITY democrats-homeland.house.gov

The term 'Havana Syndrome' originated from a series of unexplained health incidents affecting US and Canadian embassy staff in Havana, Cuba, beginning in late 2016. The symptoms reported were consistent with neurological damage, but extensive investigations by US agencies, including the CIA and the National Academy of Sciences, have not reached a definitive conclusion about the cause. While some hypotheses suggest the involvement of directed energy weapons or other advanced technologies, no conclusive evidence has been publicly presented. The phenomenon has since been reported by US personnel in other countries, and the term is now used more broadly to describe similar cases.

• First reported in late 2016 by US and Canadian diplomats in Havana, Cuba.
• Symptoms included sudden loud noises, pressure, or vibration, followed by dizziness, ear pain, memory loss, and headaches.
• Investigations by the US government and scientific researchers have not identified a definitive cause.
• Some studies suggest possible links to directed energy weapons or other exotic technologies, but evidence remains inconclusive.
• The term 'Havana Syndrome' is now used to describe similar symptoms reported by US personnel worldwide.