Activated charcoal is a mixture of very fine charcoal particles that absorb and trap poisons or drugs and prevent them from passing into your blood. Activated charcoal is usually given once. It may also be mixed with a medicine (laxative)to help you have a bowel movement. This helps move the toxins through the gut quickly. The activated charcoal may upset your stomach, cause vomiting, diarrhea or even constipation. Your stool (feces) will usually be black for 1 to 2 days. Call your caregiver if you have any concerns about your treatment.