The level of IL-6 in long COVID-19 patients was higher than that in healthy individuals (mean difference = 5.49 pg/ml, 95% CI = 2.48–8.51, P < 0.01) in cohort studies, case–control studies (mean difference = 5.65 pg/ml, 95% CI =  − 0.33 to 11.63, P = 0.06), cross-sectional studies (mean difference = 6.11 pg/ml, 95% CI =  − 11.84 to 24.06, P = 0.5), case reports (mean difference = 30.72 pg/ml, 95% CI = 30.17–31.28, P < 0.00001), and RCTs (mean difference = 17.77 pg/ml, 95% CI =  − 16.41 to 51.95, P = 0.31). Here, IL6 is linked to COVID-19.