The effect of food on the antidotal efficacy of activated charcoal was studied in six healthy volunteers, who ingested aspirin 1000 mg, mexiletine 200 mg and tolfenamic acid 400 mg in a randomized cross-over study. Activated charcoal 25 g, suspended in water, was administered 5 min or 60 min after the drugs were taken on an empty stomach or after a standard meal. The serum concentrations and the cumulative excretion into urine of the drugs were followed for 48 h. When the drugs were taken on an empty stomach, activated charcoal given 5 min or 60 min afterwards reduced the bioavailability of the drugs by 75-98% or 10-60%, respectively. Food moderately weakened the effect of activated charcoal administered 5 min after the drugs, but when the charcoal was given 1 h later the effect was still practically the same, the reduction of absorption varying in both cases in the range of 45-85%. Thus the efficacy of charcoal given 60 min after the drugs was better after a standard meal than on an empty stomach. Presence of food in the stomach of patients with drug overdosage modifies the efficacy of activated charcoal and gives it more time to adsorb drugs in the gastrointestinal canal, possibly by slowing gastric emptying rate.