The claim that activated charcoal should be ineffective or even contraindicated in intoxication due to tolbutamide is based only on limited in vitro studies. To test the claim, the effect of activated charcoal 50 g on the absorption of tolbutamide and, as a reference, of sodium valproate, was studied in 6 healthy volunteers. Each volunteer swallowed tolbutamide 500 mg and sodium valproate 300 mg with 50 ml water 1 h after a light breakfast, and within 5 min they took in randomized order either a suspension of activated charcoal or water. The absorption of tolbutamide, calculated as the peak concentration and the area under the serum drug concentration-time curve during 0–48 h, was reduced by 90% by charcoal (p<0.001). the="" absorption="" of="" valproate="" in="" these="" conditions="" was="" reduced="" on="" average="" by="" 65%="">p<0.01). in="" each="" subject="" charcoal="" had="" a="" greater="" effect="" on="" the="" absorption="" of="" tolbutamide="" than="" of="" valproate.="" according="" to="" these="" findings="" and="" preliminary="" in="" vitro="" studies="" on="" other="" sulphonylureas="" high="" doses="" of="" activated="" charcoal="" can="" be="" recommended="" for="" the="" preventing="" the="" absorption="" of="" sulphonylureas="" in="" acute="" intoxications.="" the="" poor="" aqueous="" solubility="" of="" these="" substances="" at="" the="" gastric="" ph="" probably="" delays="" their="" gastrointestinal="" absorption,="" so="" that="" they="" may="" be="" adsorbed="" on="" to="" charcoal="" even="" given="" several="" hours="">