Antihistamine use protects from long covid (caveat: small sample size, observational)
> Long COVID and Reduced Thrombosis in Antihistamine-Treated Patients: An Observational Study in the Metropolitan Area of Barcelona
> 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.
https://pmc.ncbi.nlm.nih.gov/articles/PMC12945107/
This seems like an important avenue to conduct further studies. Possibly antihistamines could be a good thing to be taken during acute covid infection if it prevents long covid (but also, I'm not your doctors and dont be taking new medications just because of something you saw on social media)
This is another repeat finding that reinfections give people long covid at similar rates to the first infection.
The observational nature of the study means we cant infer causality. There could be confounders that explain this result. However we know from other studies that have a pre-existing condition makes long covid slightly more likely, so if people are taking antihistamines for some other reason that should make long covid go up. The fact that it actually goes down is notable.