Activated charcoal consists of small pieces of charcoal treated with gas to increase its absorbency, and it is a common emergency room treatment for poison ingestion and problems with bile flow, as well as being used to treat painful gas and decrease cholesterol levels. This type of treatment is not without its risks, however, because it involves introducing a foreign substance into the gastrointestinal (GI) tract. Most activated charcoal side effects are fairly benign, but the possibility of more severe effects is one of the reasons it should only be used under a doctor's supervision.
The most common of the activated charcoal side effects is a tendency to turn the patient's stools black. Normally, black stool is a cause for concern, but in this case, it usually only represents the charcoal clearing from the body. Other side effects are much more important to look out for. Diarrhea can often occur following this treatment, but unless it continues for a prolonged amount of time afterward, it is not a dangerous effect. Vomiting is another common side effect, but does not usually indicate a severe reaction.
Somewhat less common side effects are also related to the gastrointestinal tract. These can include constipation, as well as a swelling or pain in the stomach. Constipation is often due to the charcoal absorbing water from the GI tract, and usually doesn't require further medical attention. A doctor should be notified if the charcoal causes pain or swelling, however, since these effects can indicate a poor reaction to the treatment.
Other activated charcoal side effects involve more severe forms of the mechanisms underlying constipation. Charcoal can absorb water, and occasionally this can lead to dehydration. Persistent constipation can result in a blockage of the GI tract, which can also be dangerous if left untreated.
Allergic reactions may sometimes occur as one of the activated charcoal side effects. These reactions can cause swelling in the face, mouth, and lips, as well as breathing problems. Hives and rashes may sometimes erupt on the patient's skin as well. This type of reaction should be grounds for immediately notifying a doctor, since some allergic reactions can be life-threatening if they progress.
Swallowing the activated charcoal puts people at risk of inhaling, or aspirating the charcoal. Patients may also accidentally expel charcoal out of the stomach and into the lungs. A doctor should always be contacted if the patient suspects this has happened, since aspirating charcoal can sometimes lead to death.