Speech performance is a complex matter. We behave differently, depending on which context we're in. It's very common for stutter to increase in situations where something is at stake (e.g. a crucial communication, a perfect delivery, a new encounter, things like that). Add to that, the way we think about ourselves in situations where something is at stake influences the situation. This can be a detrimental thing, where we stress ourselves unduly. But then again, it can also be an ameliorating thing, where we help ourselves be more comfortable (sort of like what you describe, with friends). So, the key issue here *isn't* - I think - that you're doing something wrong by "thinking about what you want to say". It's completely fine to think about what you want to say. Nothing uncommon or wrong in that. But the situation might be such that your likelihood of stuttering increases no matter what, simply because you're in a context where that's very likely. Perhaps, then, it would make sense to do one of two things (or both): You could work with the mindset part of things, and see if you can't lessen the stress you might be putting on yourself in those situations - and you could try speech therapy, to see if there are some techniques available that would be of use to you. At any rate, **don't try to experiment via some measure of self-medication without consulting your doctor**.