I think it could be something with the way your body is absorbing cannabinoids...some people absorb drugs better than others. I know liver function affects serum levels of prescription drugs, so why not THC as well? So given the fact that cannabinoids are often metabolized by the liver, I could see how it's function could affect how much/how little psychoactive affect you get from ingesting oral THC...I made a batch of tea that me and a friend split...I got tore up...he said he didn't feel hardly anything....it has to be differences in metabolism....