Unfortunately there is no medication for this .. the only thing you can do is to practice aur try to make yourself comfortable in every situation.. replace the word that are hard to pronounce for you with another word with similar meaning or try to reframe the sentence.. just do yoga and meditation .. do what makes you happy for a short period of time everyday to release stress in your mind ... stay calm .. remove all garbage from your mind like you may stammer while speaking and blah blah .. just don't run out of your breath while speaking.. take deep breath before speaking .. try counselling session by speech therapists they will help you