For individuals using tracheoesophageal or esophageal speech, botulinum toxin may be injected to improve voice quality when spasms or increased tone (hypertonicity) is present at the level of the pharyngoesophageal segment muscles. The amount of botulinum toxin administered unilaterally into two or three sites along the pharyngoesophageal segment varies from 15 to 100 units per injection. Positive voice improvements are possible after a single injection, however outcomes are variable. Dosages may need to be re-administered (individual-dependent) after a number of months, where effective results are expected to last for about 6 to 9 months.