<qa>  What is the NMDA receptor blocker?Our hypothesis is that dextromethorphan, an NMDA receptor blocker, will reduce voice breaks in spasmodic dysphonia to a greater degree than lorazepam, which has similar sedating side effects, but does not affect NMDA receptors with a different mechanism. On the other hand, patients with other idiopathic voice disorders, muscular tension dysphonia and vocal tremor, are hypothesized not to have a similar benefit from dextromethorphan. During the double-blind randomized cross-over study, three groups will be included, 10 patients with adductor or abductor spasmodic dysphonia, 10 with muscular tension dysphonia and 10 with vocal tremor. The results will determine if dextromethorphan has potential as a treatment option for patients with adductor or abductor SD. 