Vivitrol is a prescription medicine from Alkermes PLC that uses&nbsp;naltrexone. Naltrexone is also an opioid antagonist, blocking the&nbsp;brain's opioid receptors so users cannot feel any high from drugs. Vivitrol is taken as a monthly shot for those looking to treat opioid dependence and requires patients be opioid-free for at least a week to avoid sudden opioid withdrawal.The company has received criticism for its attempts to market its product to law enforcement and legislators as a better alternative to Suboxone and methadone medications without a study comparing Vivitrol to them, according to The New York Times.