Synthetic oil right for me?

I have a 94 chevy pick up c1500 4.3L V6 TBI Vortec. It has around 200k mi. I changed the oil yesterday to synthetic i dont see any leaks and no problems running. But will this screw up my engine? my friend said that it will do something to my cilinder or something so im startin to worry! what are disadvantiges for my pickup on synthetic oil