Long COVID and Reduced Thrombosis in Antihistamine Treated Patients: An Observational Study… 2026, Puigdellívol-Sánchez+

[SNT Gatchaman]

Long COVID and Reduced Thrombosis in Antihistamine Treated Patients: An Observational Study in the Metropolitan Area of Barcelona

Spoiler: Authors

Anna Puigdellívol-Sánchez; Antonio Arévalo-Genicio; M Carmen García-Arqué; Marta Gragea-Nocete; Celia Lozano-Paz; Vanessa Moro-Casasola; Cristina Pérez-Díaz; Roger Valls-Foix; Ramon Roca-Puig; Maria Llistosella

BACKGROUND
Early evidence from a nursing home in Yepes (Toledo, Spain) indicated that antihistamines combined with azithromycin prevented deaths and hospitalizations during the first COVID-19 wave. Subsequent data from the Consorci Sanitari de Terrassa (CST) showed that patients chronically taking antihistamines significantly reduced hospital admissions and mortality. However, a concerning rise in long COVID incidence (2–5%) after the third infection and a doubling of thrombosis rates in patients over 60 were observed.

OBJECTIVE
This study aimed to determine whether chronic antihistamine prescription is associated with a reduction in long COVID syndrome and thrombotic events.

METHODS
We analyzed anonymized data from the CST population (n=192,651 as of March 2025). Variables included age, gender, chronic antihistamine use, number of chronic treatments (nT), COVID-19 vaccination status, SARS-CoV-2 infection history, long COVID (LC) incidence, and aggregated thrombotic events. Odds ratios (OR) were calculated using chi-square tests.

RESULTS
The prevalence of LC increased progressively with successive infections in the non-antihistamine group. No significant differences were found with the antihistamine group, which presented no LC cases among the 52 patients with three documented infections. Thrombotic events were significantly less frequent in antihistamine users with at least one chronic prescription (p< 0.0001).

CONCLUSIONS
Results suggest a protective effect of antihistamines against thrombotic events. While confirmation via multicenter, randomized trials is needed, a pragmatic approach using antihistamines could be considered for symptomatic patients in the early stage of infection.

Web | DOI | PDF | Preprints.org | Open Access

 

[SNT Gatchaman]

Now published as —

Long COVID and Reduced Thrombosis in Antihistamine-Treated Patients: An Observational Study in the Metropolitan Area of Barcelona

Spoiler: Authors

Puigdellívol-Sánchez, Anna; Arévalo-Genicio, Antonio; García-Arqué, Mª Carmen; Gragea-Nocete, Marta; Lozano-Paz, Celia; Moro-Casasola, Vanessa; Pérez-Díaz, Cristina; Valls-Foix, Roger; Roca-Puig, Ramon; Llistosella, Maria

BACKGROUND
Early evidence from a nursing home in Yepes (Toledo, Spain) indicated that antihistamines combined with azithromycin prevented deaths and hospitalizations during the first COVID-19 wave. Subsequent data from the Consorci Sanitari de Terrassa (CST) showed that patients chronically taking antihistamines had significantly reduced hospital admissions and mortality. However, a concerning rise in long COVID incidence (2–5%) after the third infection and a doubling of thrombosis rates in patients over 60 were observed.

OBJECTIVE
This study aimed to determine whether chronic antihistamine prescription is associated with a reduction in long COVID syndrome and thrombotic events.

METHODS
We analyzed anonymized data from the CST population (n = 192,651 as of March 2025). Variables included age, gender, chronic antihistamine use, number of chronic treatments (nT), COVID-19 vaccination status, SARS-CoV-2 infection history, long COVID (LC) incidence, and aggregated thrombotic events. Odds ratios (OR) were calculated using chi-square tests.

RESULTS
The prevalence of LC increased progressively with successive infections in the non-antihistamine group. No significant differences were found with the antihistamine group, which presented no LC cases among the 52 patients with three documented infections. Thrombotic events were significantly less frequent in antihistamine users with at least one chronic prescription (p < 0.0001).

CONCLUSIONS
Results suggest a protective effect of antihistamines against thrombotic events. While confirmation via multicenter, randomized trials is needed, a pragmatic approach using antihistamines could be considered for symptomatic patients in the early stage of infection.

Web | DOI | PDF | Viruses | Open Access

 

[Hutan]

This is sort of interesting. I vaguely recall that my daughter, who was initially hospitalised for a few days with the gastrointestinal infection that seemed to trigger ME/CFS in her, her brother and in me was said to have had eosinophilia, and so I have wondered about there being some allergy-ish process being involved.

But, from the abstract, I can't tell if the Long Covid definition is likely to be particularly relevant to ME/CFS. Maybe it is more about tissue damage arising from severe illness.

Also, maybe the risk of Long Covid was actually higher in the group that were taking anti-histamines versus the group that was not? The abstract is very unclear.

CONCLUSIONS
Results suggest a protective effect of antihistamines against thrombotic events. While confirmation via multicenter, randomized trials is needed, a pragmatic approach using antihistamines could be considered for symptomatic patients in the early stage of infection.

The conclusions don't suggest that they found any protective effect of antihistamines against Long Covid - only possibly against thrombotic events.

 

[Hutan]

The Data Analysis Control Department collected anonymized data from the entire CST population without exclusions. This included information on COVID-19 infections, hospital admissions, long COVID syndrome (LC), and thrombotic events (Thr)—including strokes, myocardial infarction, pulmonary thromboembolism, and retinal vessel thrombosis—from March 2020 to March 2025.

Ha, as I expected, they would have told us about some protective effect against Long Covid in the abstract if they had found one. They didn't tell us about such an effect and they didn't find one.

Adding up the numbers in Table 1, the rate of Long Covid in the no antihistamine group was 12.31%. The rate of Long Covid in the antihistamine group was 12.53%.

Antihistamines during the infection certainly is not a smoking gun against Long Covid.

I think the authors of this paper have presented their results in a misleading way, by focussing on what happened in the very small group of people who had antihistamines at the time of their third infection, rather than looking at what the overall numbers involving thousands of people are telling us.

Possibly, this study as counts as evidence against the MCAS theory of Long Covid and ME/CFS, and even against the idea of antihistamines as therapy for ME/CFS, although it's not strong evidence.