I would say that it usually lasts at least a day, but sometimes I notice that it lasts 2-3 days (or even a week on rare occasions) depending on the circumstances. It's hard to say because serotonin and dopamine levels change depending on stress or worry in my life, rate-limiting (eg if the body runs out of certain ingredients to create serotonin), etc. I don't think there's a cure, at least not yet. And 5-htp is definitely not a cure, so we may need to take it for the rest of our lives as long as the chemical imbalance exists. (I'm only speaking about my own stuttering where I think it is due to an imbalance of dopamine and serotonin). That being said, I feel that as I get older, my hormone and neurotransmitter levels (including serotonin and dopamine) are starting to balance itself out. I no longer need to take 5-htp every day and my fluency is still ok or adequate when I don't take 5htp. I'm still more prone to stuttering when I don't take 5htp, but it's not as bad as before. I can now have adequate fluency for days, sometimes 1-2 weeks, without taking 5-htp. But my life is also less stressful and more carefree now, so that definitely is a contributing factor.