Naltrexone typically starts working within 1 to 2 hours after taking it, whether taken orally or by injection. Oral naltrexone absorbs quickly, with effects beginning around one hour after ingestion. The injectable form (such as Vivitrol) may take about 2 hours to start working, with full effects potentially taking a few days. The medication works by blocking opioid receptors, which helps reduce cravings for opioids and alcohol, making these substances less enjoyable and thus aiding in addiction treatment. The craving reduction effects usually last about 24 hours for oral doses and up to a month for the injectable version.
