The recommended dosage is 250-600mg. Always start with a lower one and once you get used to it, you can increase the dosage. If you're taking it long term, you have to cycle it on and off as well. It definitely does make you sleepy cause it improves sleep quality and high dosage can also lead to frequent headaches. Never take more than the recommended one. It probably won't make you completely fluent, but does help with stress which may improve stuttering as you become more relaxed and gain confidence. There's another supplement called L-Theanine which also helps with anxiety, relaxation and sleep. You can look into that as well. You have to note that supplements aren't a cure and some of them may only have short term placebo effects. So, it may or may not help you improve your stutter which varies from person to person.