Hydrocodone, sold under the brand name Zohydro ER, among others, is an opioid used to treat severe pain of a prolonged duration, if other measures are not sufficient. It is also used as a cough suppressant in adults. It is taken by mouth. Typically it is sold as the combinations acetaminophen/hydrocodone or ibuprofen/hydrocodone. By itself it is sold in a long-acting formulation.Common side effects include dizziness, sleepiness, nausea, and constipation. Serious side effects may include abuse, low blood pressure, seizures, QT prolongation, respiratory depression, and serotonin syndrome. Rapidly decreasing the dose may result in opioid withdrawal. Use during pregnancy or breastfeeding is generally not recommended. Hydrocodone is believed to work by activating opioid receptors, mainly in the brain and spinal cord. Hydrocodone 10 mg is equivalent to about 10 mg of morphine by mouth.Hydrocodone was patented in 1923, while the long-acting formulation was approved for medical use in the United States in 2013.