Havana Syndrome: Cholinesterase Overexposure Hypothesis Among Canadian Diplomats

SUMMARY

Beginning in 2016, Canadian diplomats and their family members stationed in Havana, Cuba, reported experiencing a range of unexplained neurological symptoms, mirroring those reported by U.S. personnel. A peer-reviewed study, 'Havana syndrome among Canadian diplomats: brain imaging reveals acquired neurotoxicity,' published in *Brain Repair Centre* and initially posted on MedRxiv, posits that these symptoms and associated brain injuries are consistent with overexposure to cholinesterase inhibitors, suggesting a neurotoxin etiology. This study involved multimodal examinations of 26 affected individuals.

While this specific paper presents evidence supporting the cholinesterase overexposure hypothesis for the Canadian cases, broader investigations into Havana Syndrome have yielded conflicting results. For instance, more recent studies published in *JAMA* involving a larger cohort of U.S. and Canadian personnel have reportedly found few significant differences in cognitive and physical tests between affected individuals and control groups, suggesting alternative explanations or casting doubt on a singular biological cause across all cases. The scientific community remains divided on the precise etiology of Havana Syndrome, with the cholinesterase hypothesis being one proposed explanation among several.

CLAIMS

1. SINGLE-SOURCECONF 0.90

   Brain imaging of Canadian diplomats affected by Havana Syndrome revealed acquired neurotoxicity consistent with overexposure to cholinesterase inhibitors.

   — attributed to: Brain Repair Centre, Dalhousie University, Life Sciences Research Institute (via a research report and pre-print)

   • https://journals.sagepub.com/doi/10.1177/00207640231208374
   • https://www.medrxiv.org/content/10.1101/19007096v1.full-text
   • https://www.medrxiv.org/content/10.1101/19007096v1.full.pdf
   • https://www.researchgate.net/publication/336180266_Havana_Syndrome_Among_Canadian_Diplomats_Brain_Imaging_Reveals_Acquired_Neurotoxicity
2. VERIFIEDCONF 0.95

   The study included multimodal examinations of 26 Canadian diplomats and their family members experiencing Havana Syndrome symptoms.

   — attributed to: Research report 'Havana syndrome among Canadian diplomats: brain imaging reveals acquired neurotoxicity'

   • https://www.researchgate.net/publication/336180266_Havana_Syndrome_Among_Canadian_Diplomats_Brain_Imaging_Reveals_Acquired_Neurotoxicity
3. VERIFIEDCONF 0.95

   Canadian diplomats and their families stationed in Havana showed significantly lower white matter integrity compared to non-exposed diplomats and healthy controls.

   — attributed to: Research report 'Havana syndrome among Canadian diplomats: brain imaging reveals acquired neurotoxicity'

   • https://pmc.ncbi.nlm.nih.gov/articles/PMC9050567/
4. CORROBORATEDCONF 0.80

   Canadian diplomats who worked in Cuba are suing the Canadian government for $28 million for failing to address the Havana Syndrome issue.

   — attributed to: News reports and forum discussions

   • https://www.reddit.com/r/UnresolvedMysteries/comments/cj5ilp/havana_syndrome_what_is_the_mysterious_noise/
   • https://www.reddit.com/r/canada/comments/ao3uw6/havana_syndrome_canadian_diplomats_who_worked_in/
5. SINGLE-SOURCECONF 0.70

   Two studies published in JAMA found few significant differences in cognitive and physical tests among more than 80 Havana Syndrome patients (U.S. and Canadian) compared with a control group.

   — attributed to: A Reddit post referencing NIH findings

   • https://www.reddit.com/r/EverythingScience/comments/1bhrtq1/nih_probe_of_havana_syndrome_finds_no_sign_of/
6. SINGLE-SOURCECONF 0.60

   Havana Syndrome, for some, has been characterized as a 'mass delusion.'

   — attributed to: A Reddit user

   • https://www.reddit.com/r/skeptic/comments/11f9qbi/havana_syndrome_not_caused_by_energy_weapon_or/
7. SINGLE-SOURCECONF 0.70

   A 2019 University of Pennsylvania study (Verma, et al., JAMA) revealed neuroimaging differences in brain volumes and white-matter integrity in Havana Syndrome patients.

   — attributed to: Len Berman, Substack post

   • https://lenbermd.substack.com/p/tainted-2024-nih-study-on-havana

TIMELINE

• 2016U.S. and Canadian diplomats begin reporting unexplained neurological symptoms in Havana, Cuba. [src]
• 2019-09-29Pre-print of 'Havana syndrome among Canadian diplomats: brain imaging reveals acquired neurotoxicity' is published on MedRxiv, proposing cholinesterase overexposure. [src]
• 2019-10-04News outlets report on the Canadian study suggesting pesticide poisoning as a cause for 'Havana syndrome' injuries. [src]
• 2023-10-18Peer-reviewed article 'Havana syndrome among Canadian diplomats: brain imaging reveals acquired neurotoxicity' is published in *Brain Repair Centre*. [src]

ENTITIES

• ORG Brain Repair Centre, Dalhousie University — Research Institution that published a study on Canadian diplomats
• PERSON Canadian diplomats — Individuals affected by Havana Syndrome symptoms
• PLACE Havana, Cuba — Location where incidents occurred
• EVENT Cholinesterase Inhibitors — Proposed etiology of symptoms
• ORG University of Pennsylvania — Institution that conducted a 2019 study on Havana Syndrome
• ORG JAMA — Journal where studies on Havana Syndrome have been published
• PERSON U.S. Diplomats — Individuals also affected by Havana Syndrome symptoms

OPEN QUESTIONS — PENDING LEADS

• Are there other peer-reviewed studies besides the 'Havana Syndrome Among Canadian Diplomats' paper that corroborate the hypothesis of cholinesterase overexposure in any 'Havana Syndrome' cases?
• Identify the specific 'JAMA' studies referenced in Reddit discussions that found 'few significant differences' in Havana Syndrome patients compared to controls, and analyze their methodologies.
• Are there any declassified government reports or official statements from Canadian or U.S. authorities that specifically address the cholinesterase overexposure hypothesis?
• What is the current status of the lawsuit filed by Canadian diplomats against their government regarding Havana Syndrome?
• Are there any peer-reviewed studies that specifically refute the cholinesterase overexposure hypothesis with direct evidence?

EVIDENCE — CAPTURED SOURCES

1. [WEB] https://www.medrxiv.org/content/10.1101/19007096v1.full-text

   29 Sept 2019 · Our findings confirm brain injury, specify the regions involved, and raise the hypothesis of overexposure to cholinesterase inhibitors as a plausible etiology.

2. [WEB] https://journals.sagepub.com/doi/10.1177/00207640231208374 [archived]

   Havana syndrome among Canadian diplomats: brain imaging reveals acquired neurotoxicity (Research Report). Brain Repair Centre, Dalhousie University, Life Sciences Research Institute.

3. [WEB] https://www.researchgate.net/publication/362670044_Havana_syndrome_a_scoping_review_of_the_existing_literature

   Request PDF | Havana syndrome: a scoping review of the existing literature | Since 2016, numerous American and Canadian diplomats and secret (intelligence) agents in Cuba, China, and other places ...

4. [WEB] https://www.medrxiv.org/content/10.1101/19007096v1.full.pdf [archived]

   29 Sept 2019 · We report clinical, imaging, biochemical, and toxicological evidence consistent with the hypothesis of overexposure to cholinesterase inhibitors ...

5. [WEB] https://pmc.ncbi.nlm.nih.gov/articles/PMC9050567/ [archived]

   The findings presented in this work demonstrate that the Canadian diplomats and their families who were stationed in Havana show significantly lower WM integrity relative to a cohort of non-exposed diplomats and healthy controls.

6. [WEB] https://www.facebook.com/NeuroNewsResearch/posts/canadian-diplomats-with-havana-syndrome-injuries-show-signs-of-pesticide-poisoni/2767267606625313/

   4 Oct 2019 · Canadian diplomats with “Havana syndrome” injuries show signs of pesticide poisoning, suggests a new international study.

7. [WEB] https://lenbermd.substack.com/p/tainted-2024-nih-study-on-havana [archived]

   Following the "outbreak" of Havana Syndrome among diplomats and spies starting in 2016, brain researchers at the University of Pennsylvania (UPenn) conducted a study (Verma, et al., JAMA 2019) which revealed neuroimaging differences in brain volumes and white-matter integrity.

8. [REDDIT] https://www.reddit.com/r/TargetedEnergyWeapons/comments/yts34b/wiki_dew_havana_syndrome_medical_studies/ [archived]

   [J] [Diplomats] [Symptoms: Vestibular] Proposal for a new diagnosis for U.S. diplomats in Havana, Cuba, experiencing vestibular and neurological symptoms. (2019)

9. [REDDIT] https://www.reddit.com/r/EverythingScience/comments/1bhrtq1/nih_probe_of_havana_syndrome_finds_no_sign_of/ [archived]

   Two studies, published Monday in JAMA, found few significant differences in a range of cognitive and physical tests among more than 80 patients who had been stationed in Cuba, Austria, China and other locations compared with a control group of people with similar job descriptions…

10. [REDDIT] https://www.reddit.com/r/worldnews/comments/1bsqu2r/5year_havana_syndrome_investigation_finds_new/ [archived]

    It's not like the skyscrapers, massive tunnel systems, incredible mines literally miles deep, massive infrastructure for all modern technology, and the interconnected network of goods and resources that traverses the globe in ever-increasing complexity, among effectively uncounta…

11. [REDDIT] https://www.reddit.com/r/OutOfTheLoop/comments/1bu2k7h/what_is_going_on_with_havana_syndrome/ [archived]

    Here is the paper from our study. And this was our general finding: Using a multimodal, quantitative, and control-tested approach, our results confirm brain injury, specify the regions involved, and suggest a likely etiology underlying the Havana Syndrome in the form of environme…

12. [REDDIT] https://www.reddit.com/t/havana_syndrome/ [archived]

    This community is a place to share and discuss new scientific research. Read about the latest advances in astronomy, biology, medicine, physics, social science, and more. Find and submit new publications and popular science coverage of current research.

13. [REDDIT] https://www.reddit.com/r/skeptic/comments/11f9qbi/havana_syndrome_not_caused_by_energy_weapon_or/ [archived]

    Havana syndrome however was just mass delusion; whether there was anything there of substance in the beginning is even dubious. But targeted energy weapons there's not really any support.

14. [REDDIT] https://www.reddit.com/r/UnresolvedMysteries/comments/cj5ilp/havana_syndrome_what_is_the_mysterious_noise/ [archived]

    The Canadian government has confirmed 14 cases total. In February 2019, 14 affected Canadians (5 diplomats and their dependents) sued their government for $28 million for failing to address the issue. As yet the case appears to be in progress.

15. [REDDIT] https://www.reddit.com/r/canada/comments/ao3uw6/havana_syndrome_canadian_diplomats_who_worked_in/ [archived]

    'Havana Syndrome': Canadian diplomats who worked in Cuba suing Ottawa for $28M

16. [WEB] https://www.researchgate.net/publication/336180266_Havana_Syndrome_Among_Canadian_Diplomats_Brain_Imaging_Reveals_Acquired_Neurotoxicity [archived]

    16 Jan 2026 · METHODS: We conducted a multimodal study examining 26 Canadian diplomats and their family members, the majority of whom presented with symptoms ...

CROSS-REFERENCE

• → SHARES-EVENT Havana Syndrome: Anomalous Health Incidents Intelligence Community Assessments and Disputes — This dossier concerns the same overarching 'Havana Syndrome' incidents, but focuses on the Canadian cohort and a specific etiological hypothesis.
• ← SHARES-ACTOR Havana Syndrome: Russian Intelligence and Acoustic Weapons Allegations — Both reference U S Diplomats, Canadian Diplomats