Antihistamine and COVID-19 outcomes in outpatients.

The World Health Organization declared the coronavirus disease 2019 (COVID-19) pandemic on March 11, 2020. Since then, researchers have been investigating the efficacy and side effects of its medication, up until now. From the viewpoint of Persian medicine, some medications such as antihistamines may cause retention of secretions and lead to exacerbation and spread of the disease in the body. There are studies with conflicting results regarding the effectiveness of antihistamines in COVID-19. Systematic reviews found a lack of data on beneficial effect of antihistamine-decongestant-analgesic combinations for the common cold and a limited short-term effect of antihistamines on severity of overall symptoms. This prospective cohort study was designed to investigate the relationship between the use of antihistamines and the severity of COVID-19 symptoms. Three hundred patients with a diagnosis of COVID-19 participated in the study in Shiraz, Iran from December 4, 2021 until January 24, 2022. The interviews were conducted via phone call by a single interviewer. Patients were followed weekly for 4 weeks. We collected information by using a data collection form, containing demographic information, underlying disease, COVID-19 symptoms, treatment methods, medications, and a list of antihistamines and herbs that might have been used. Generalized estimating equations were applied to assess the relationship between the severity of COVID-19 and the use of antihistamines, taking into account potential confounding factors such as time and herbal consumption. The difference in the severity of COVID-19 disease in antihistamine users compared to nonusers was not significant in 4 weeks despite the higher baseline severity in nonusers. The comparison of two groups of antihistamine users and nonusers showed that there was a significant difference (p = 0.001) regarding the use of herbal medicines.