Yes, works very fast. Mix some Activated Charcoal in some juice, about a Teaspoon, let it fall to the bottom before mixing and drinking because it floats and any vigorous mixing bfore it sinks will have it all over the place. Also works for stomach upsets, gas and vomiting. Vomiting may take up to 3 doses but it will work, be prepared as black Charcoal Vomit is awful if you miss the bag or toilet.
Those with negative effects probably took too much, didn't drink enough water, didn't counter with extra fiber from veggies, fruits or fiber supplements. I had a little constipation. Stools were a little dry and hard to pass. So I backed down from a teaspoon 2 or 3 times a day, to 1/2 a tsp. 2 or 3 times a day, and made sure to drink plenty of water and eat enough fiber from foods and I also followed the charcoal with slippery elm, about a tablespoon in a pint of water, which makes a thin mucilaginous drink that is soothing to the gi tract and moves things on through it. I have had great results. Totally stopped the bout of gas and diarrhea that I had hit me, I guess from a bug or food poisoning.
Raw Activated Charcoal, works like a dream for diarrhea, in hours not days.