i have done meph alot of times, once doing 12g in a week, and i have never really experienced any negative side effects. The only things i dislike about the drug is how fiendish it is, that horrible feeling of complete dispair when you run out and the comedown the next day. Although i find usually the comedown is largely due to a lack of sleep as many times i have done it during the day, stopped at about 9ish had a few drinks got a full nights sleep and felt completely fine the next day. I also don't find mephedrone to be a very addictive drug; sure at the time theres nothing you want more but the next day theres no real urge to redose ( i know that may sound silly coming from me seeing as i did 12gs in a week and i'll admit i did get a bit carried away but when i felt it got too much and lost too much weight there was no trouble stopping even with a g or 2 sitting in my room still)