Apparently activated charcoal will absorb the caffeine but it also absorbs enough codeine that it is not worth it. And it doesn't get rid of all the caffeine either, so it's not ideal.
hmm i've got about 3 grams of codeine with acetaminophen and caffeine in pills is there any way to measure or estimate how much codeine and caffeine would be lost in a charcoal filter?because with that much i could lose a gram or two even and still get high a couple times as i have no tolerance and i could use a brita water filter right?