Benefits
Less intestinal gas after a gas-producing meal
In a placebo-controlled study, oral activated charcoal prevented the large rise in flatus events and breath hydrogen that normally follows a gas-producing meal. A double-blind trial in 99 people in the United States and India also found lower breath hydrogen than placebo after lactulose. A study in five volunteers taking 0.52 g four times daily found no change in fecal gas release.
Less bloating and cramping in a lactulose gas test
In a double-blind trial of 99 people given lactulose, bloating and abdominal cramps attributed to gas were significantly lower with activated charcoal than with placebo in both the US and Indian groups. A study in five volunteers found no change in abdominal symptoms after one week of charcoal. The positive trial's abstract does not report the dose.
Mechanism of action
Nonspecific surface binding
Activated charcoal has a very large surface area that lets it bind many drugs and toxins inside the digestive tract and reduce how much is absorbed. Non-ionized organic compounds bind better than dissociated inorganic ones, and metals such as iron and lithium salts are not suited to charcoal treatment.
Enhanced elimination with repeated clinical doses
In hospital care, repeated doses of charcoal are used to speed removal of some drugs already in the body. An international toxicology consensus lists this use for carbamazepine, cardiac glycosides, colchicine, dapsone, phenobarbital, phenytoin, thallium and theophylline. This is emergency medicine, not a supplement use.
Little gas binding inside the gut
Researchers who measured fecal gas reported that charcoal binds little of the main gut gases by volume. Sulfur gases that cause odor should bind well, but ingested charcoal did not reduce their release, probably because its binding sites fill up during passage through the gut.
Clinical trials
Placebo-controlled trial; the abstract does not describe the participants or the dose (Hall et al. 1981, Am J Gastroenterol)
Participants ate a gas-producing meal with activated charcoal or with placebo. The number of flatus events and breath hydrogen concentration were measured.
Oral activated charcoal prevented the large increase in flatus events and breath hydrogen concentration that normally follows a gas-producing meal.
Double-blind, placebo-controlled trial; the abstract does not state the dose (Jain et al. 1986, Am J Gastroenterol)
99 people in the United States (n = 30) and India (n = 69), two groups known to differ in diet and gut flora, given lactulose to produce colonic gas.
Compared with placebo, activated charcoal significantly lowered breath hydrogen (p < 0.05) in both groups and significantly reduced bloating and abdominal cramps attributed to gas.
Before and after study with no placebo group, plus in vitro binding tests; US government funded (Suarez et al. 1999, Am J Gastroenterol)
Five healthy volunteers took 0.52 g of activated charcoal four times daily for one week; fecal gas release was measured before and after.
No significant reduction in fecal release of any sulfur-containing gas, in total fecal gas release, or in abdominal symptoms. In vitro tests suggested charcoal binding sites become saturated during passage through the gut.
Systematic review by the Clinical Toxicology Recommendations Collaborative, GRADE assessed, databases searched to December 2019; emergency medicine context, not a supplement use (Hoegberg et al. 2021, Clin Toxicol (Phila))
296 human, 118 animal and 145 in vitro studies of oral activated charcoal in poisoned adults and children, plus 71 human and 2 animal studies reporting adverse events.
469 studies (83%) were rated Low or Very Low GRADE. The 90 Moderate or High GRADE studies covered paracetamol, phenobarbital, carbamazepine, cardiac glycosides, ethanol, iron, salicylates, theophylline, tricyclic antidepressants and valproate. Data were heterogeneous; the clinical studies reported a benefit of charcoal given beyond one hour in many scenarios.
Randomized, unblinded controlled trial at The Canberra Hospital, Australia; emergency medicine context (Cooper et al. 2005, QJM)
327 adults presenting with an oral overdose, randomized to activated charcoal or no decontamination. Late presenters and very serious ingestions (at the physician's discretion) were excluded.
No difference in length of stay (6.75 h with charcoal vs 5.5 h without, p = 0.11) or in vomiting, mortality or intensive care admission. There were few adverse events. The authors note this does not exclude a role soon after ingestion of highly lethal drugs.
Nonrandomized crossover study; charcoal was given with magnesium citrate (Katona et al. 1989, J Toxicol Clin Toxicol)
Eleven healthy men aged 21 to 37 enrolled and nine completed. They drank 0.6 g/kg ethanol, and on a second occasion after at least a week also took 60 g of superactive charcoal with 300 ml of magnesium citrate solution at 1 hour and again at 3 hours.
Charcoal did not significantly change blood ethanol area under the curve (1167 with charcoal vs 1184 mcg x hr/ml without) or the highest ethanol level (49.0 with charcoal vs 46.3 mg/dl without); levels were significantly lower only at the 2 hour sample (31.6 vs 36.6 mg/dl). Volunteers had difficulty finishing the second 60 g dose.