I think you may be thinking of the old days when NAC was an oral medication. Charcoal would adsorb our antidote in that case. Now NAC can be given IV, safe from the GI charcoal.
Well, if they are unconscious, you can try charcoal only if you intubate them. If they are sleepy but not intubated, then nothing. You don't want the patient to aspirate the charcoal.