Friend doesn't stutter on ketamine, but I still do. Neurological difference or something else?

Friend doesn't stutter on ketamine, but I still do. Neurological difference or something else? A friend and I both have moderate to severe to stutters. He did ketamine treatment for depression a few years ago and I'm seeing how it goes with my depression. Does anyone happen to know why he's fluent during a trip (I'm guessing it's anxiety related?) but I'm not? I have a lot harder time relaxing and letting go of control, which makes my trip tolerable but not something I count down the days to.