I've used one but tbh, I have no idea what effect it had. I smoked from a bong that had 3 percs, an ice catcher, a perc ash catcher AND a carbon filter.... needless to say I barely felt the smoke going into my lungs. My boyfriend hates smoking from anything with a filtration system and claims it doesn't get him as high but I feel the opposite... the smoother the smoke for me, the more and longer I can hold it in my lungs. I don't know if it removes much of the thc but I would think it's just like any other filtration system.