I started off/on last five years after not using it in high school (1982). It really messes your lungs up even if you try to filter it. The natural reaction of the lungs (to irritation) is to produce extra phlegm. If I stop smoking it takes me 3-5 wks before my lungs stop producing extra mucus. Vaporizing, edibles would be best alternative. I've tried filtering a bong (for toxins) with active carbon but only slightly helps. There are like 37 toxins in marijuana smoke so this Nat'l. medical marijuana experiment is a complete sham and is going to have huge health and economic fallout.