Naltrexone is approved by the Food and Drug Administration (FDA) The pill form of naltrexone can be taken at 50 mg once per day. The injectable form of the drug (Vivitrol) is administered at 380 mg intramuscular once a month. Naltrexone can be prescribed by any health care provider who is licensed to prescribe medications. To reduce the risk of precipitated withdrawal, patients are warned to abstain from illegal opioids for a minimum of 7-10 days before starting naltrexone. If switching from methadone to naltrexone, the patient has to be completely withdrawn from the opioids.
