A stutter can be caused by neurological disorders, TBI’s, and even autoimmune diseases. If not caused, in some cases, then at least those are a contributing factor. Me personally, I never stuttered until I was using certain drugs on the daily every day. The stutter lasted for the duration of the high and went away afterward, but over the course of my 2 year addiction period it would still remain even during the comedown and after sobering up. When I ended up ODing 4 years ago, I woke up in the ER first unablw to speak then later the ICU and had a prominent stutter with major blocks. The doctors there never were able to diagnose it, but I imagine that I experienced hypoxia or similar and suffered neurological damage similar to a TIA or stroke due to losing consciousness Since then 4 years ago, I’ve made progress in healing but still have moderate speech blocking and a mild stutter which are both improved temporarily with my adhd medication (amphetamines). I’ve been sober off my drug of choice now for 2 years too :) I’d say in my case though that neurological damage was 100% part of the cause