The blocking occurs because of anxiety, a frustration at stuttering. When you don't want to say "b-b-b-bread", you force yourself to be able to say the rest of the word, which gradually turns into a blockage. To resolve this problem, it is a job on you. You either have to be willing to say "b-b-b-bread", even if it's a bit frustrating, or find other ways to be more fluent (although there is debate about whether you should use these methods, because they don't always work and can increase the idea that stuttering = wrong) these methods are slowing down, speaking in syllabics, pauses, airflow, Erasm... plenty of content online explains each method in detail. As a result, there are no direct medications to reduce blocking, which is a secondary behavior of stuttering. There is some for anxiety, some medications have been shown to reduce stuttering, but are not currently approved to treat it, so back to acceptance or fluency techniques