Dharia I, et al. - Since the primary treatment of adductor spasmodic dysphonia was repeated injections of botulinum toxin type A (Botox) into the thyroarytenoid muscles, researchers conducted this retrospective study to assess the treatment impact and side effect profile across a large number of injections. This research was previously performed on 45 patients in 2002. The sample consisted of all individuals (n = 272) with adductor spasmodic dysphonia with and without tremor treated by the senior laryngologist at George Washington University. For each patient after each injection, duration of effects and side effects (vocal weakness and liquid dysphagia) were recorded into a database. Compared with the unilaterally injected individuals, optimal effect duration (≥ 3 months) was more commonly seen in the bilaterally injected individuals. Compared with the bilaterally injected individuals, optimal side effect duration (≤ 2 weeks) was better for the unilaterally injected patients. Compared with the unilaterally injected individuals, having both optimal effect and side effect in the same injection was more commonly seen in the bilaterally injected individuals. In producing optimal effect/side effect profiles, bilateral injections of Botox were more effective.