 Postictal apnea could partly derive from a seizure-induced massive release of endogenous opioids. Animal studies suggest that such seizure-related release of endogenous opioid peptides participate to termination of seizures. In patients with epilepsy, functional imaging studies have confirmed that seizures induce release of endogenous opioids. The brainstem respiratory centers contain the highest density in opioid receptors, accounting for respiratory depression being one of the cardinal symptoms of opioid overdose. 