The objective of the study was to estimate the effect of activated charcoal (AC) administered during the first 6 h after drug intake and the effect of drug properties on drug exposure. Sixty-four controlled studies were integrated in a meta-analysis. AC administered 0-5 min after administration of a drug reduced median drug exposure by 88.4% (25-75 percentile: 65.0-96.8) (P < 0.00001). The effect of AC continued to be statistically significant when administered up to 4 h after drug intake (median reduction in drug exposure 27.4% (range 21.3-31.5%, P = 0.0006). The reduction in drug exposure was correlated with the AC/drug ratio (rho = 0.69, P < 0.0001), the volume of distribution (Vd) (rho = 0.46, P = 0.0001), and time to peak concentration (rho = 0.40, P = 0.02). We found that AC is most effective when given immediately after drug ingestion but has statistically significant effects even when given as long as 4 h after drug intake. AC appears to be most effective when given in a large dose.