Sophie Medlin in Popular Science:
On her Goop website, Gwyneth Paltrow claimed that charcoal lemonade was one of the “best juice cleansers”. That was in 2014. Today, charcoal products—from croissants to capsules—are everywhere. Even high street coffee chains have taken to selling charcoal “shots”.
Some vendors of these products claim that activated charcoal can boost your energy, brighten your skin and reduce wind and bloating. The main claim, though, is that these products can detoxify your body.
It’s easy to see where the claim that activated charcoal can detoxify the body comes from: it is used in emergency medicine to reduce the toxic load when someone has consumed poison or overdosed on medication. Charcoal binds to poison in the gastrointestinal tract and stops it from being absorbed into the bloodstream. The toxins are then passed out of the body in the stool.
However, this detoxifying action is another case of the non-scientific nutritionists seeing the medical use for something and misinterpreting its application.
More here.