creatine has been around for a long time, and long term studies have been done. Yes, creatine is found in meat, but in small amounts, not enough to create the results that creatine in supplement form give. All creatine does, is provide an extra source of phosphate, which will turn ADP(adenazine di-phosphate) into ATP(adenazine tri-phosphate) which is what your muscles use to work. So more ATP =heavier lifting=increased muscle gains, all of which will still be there, minus water weight, when you go off it. i recommend this site
http://www.absolute-creatine.com/ for general info. And creatine has not been conclusively shown to stop your bodies ability to produce it in the long run. the best form of creatine is creatine monohydrate, don't get any other kind
now creatine is not necessary to build muscle, but many people have found it to help in their gains, it's up to you if you want to try it out, but make sure you're fully educated on the matter