<qa>  What is a drug that alters reflexes of the larynx?This study will examine how dextromethorphan, a drug that alters reflexes of the larynx voice box, might change voice symptoms in people with voice disorders due to uncontrolled laryngeal muscle spasms. These include abductor spasmodic dysphonia breathy voice breaks, adductor spasmodic dysphonia vowel breaks, muscular tension dysphonia tight strained voice, and vocal tremor tremulous voice. Dextromethorphan-one of a group of drugs called NMDA antagonists-has been used for years in over-the-counter cough suppressant medicines. In animal studies, the drug has blocked one of the reflexes in the larynx that may be associated with spasms in the laryngeal muscles. This study will compare the effects of dextromethorphan, lorazepam a valium-type drug, and a placebo inactive substance in patients with the four types of voice disorders described above. 