Naloxone is a medication prescribed to block the effects of opioids (opioid antagonist). It is available as a generic medicine; its brand name is Narcan and it can be taken orally, via injection, through intravenous infusion, or as a nasal spray. It is usually taken to counter decreased breathing due to opioid overdose. Its effects last from 30 minutes to 1 hour and works within 2 minutes when administered intravenously while it works within five minutes when given via injection. Naloxone often has negligible effects if the patient did not take any opioid. However, for those with opioids in their systems, the side effects may include vomiting, sweating, agitation, headache, trembling, and flushing. In rare cases, it may be linked with seizures, heart rhythm alterations, and pulmonary edema. In the United States, naloxone is available over the counter in all states except in Hawaii.