Overdose of activated charcoal can lead to severe constipation
Few activated charcoal supplements contain sorbitol, which acts as a laxative, and one may suffer from diarrhea
Activated charcoal can greatly hamper the medicinal drug absorption, if you are under any treatment. For example, if you are taking antidepressant medicine, charcoal supplement can nullify the action of the antidepressant drug and you may fail to get the effect of the medicine.
People under charcoal supplement often notice black tarry stools; however, it is not hazardous