Tizanidine, sold under the brand name Zanaflex among others, is a medication that is used to treat muscle spasticity due to spinal cord injury or multiple sclerosis. Effectiveness appears similar to baclofen or diazepam. It is taken by mouth.Common side effects include dry mouth, sleepiness, weakness, and dizziness. Serious side effects may include low blood pressure, liver problems, psychosis, and QT prolongation. It is unclear if use in pregnancy and breastfeeding is safe. It is an α2-adrenergic agonist and how it works is not entirely clear.Tizanidine was approved for medical use in the United States in 1996. It is available as a generic medication. In 2017, it was the 89th most commonly prescribed medication in the United States, with more than nine million prescriptions.