This is true but it should be clarified that the charcoal given in emergency medical treatment is “activated” charcoal and that it is only helpful against certain types of poisons. A dramatic example of this is the tale of Professor Touery, who in 1831 in front of his colleagues at the French Academy of Medicine ingested 15 grams of the deadly poison strychnine (that is ten times the lethal dose). He lived to tell the tale because he mixed the strychnine with activated charcoal.
Activated charcoal is charcoal that had been processed to make it even more porous than normal charcoal. This gives the charcoal even more surface area. A single gram of activated charcoal can have a surface area of 1000 m2 **. (In terms most Americans will understand better, 1 lb of activated charcoal has the same surface area as 84.8 football fields) It is this vast surface area that allows the charcoal to adsorb poisons and other substances. When a material adsorbs something, it attaches to it by chemical attraction. The vast surface area of activated charcoal gives it a countless number of bonding sites. This is why activated charcoal helps to prevent the poison from being absorbed into the body. But it won’t adsorb everything, activated charcoal isn’t effective in bonding to :
- Lithium (Eskalith, Lithobid), strong acids and bases, metals and inorganic minerals such as sodium, iron, lead, arsenic, iodine, fluorine, and boric acid
- Alcohol (such as ethanol, methanol, isopropyl alcohol, glycols, and acetone)
- Hydrocarbons (such as petroleum distillates and plant hydrocarbons such as pine oil)
As such, it will not prevent these poisons from being absorbed into the body. Bummer… You can't erase a night of binge drinking by eating the wood dregs from the fireplace.
It’s a good time to point out the difference between adsorption and absorption. Adsorption is the adhesion of substances to a surface. Absorption is when a fluid permeates a solid or is dissolved by a liquid. The poison adheres to the surface of the charcoal and since the charcoal cannot be absorbed by the digestive tract, it passes out of the body.
References:
Principles of clinical toxicology By Thomas A. Gossel, J. Douglas Bricker page 53
** http://www.calgoncarbon.com/documents/ACWhatitisHowitworks.pdf