That was most likely just the placebo effect. The only medications that have demonstrated the most efficacy are anti-psychotics - which block dopamine. An hypothesis points to excessive dopaminergic activity in people who stutter. Anti-psychotics have been proven to reduce stuttering but the side-effects are so vile that it might not be worth it. The second-generation antipsychotics have lower risk of those vile side-effects but chance of getting diabetes is still high. Blood-pressure medications have shown limited efficacy. Benzos like Xanax and Klonopin can decrease the anxiety related to stuttering but the long-term use of benzos is not recommended because of tolerance and high abuse potential