NEW YORK (Reuters Health) – An extended-release version of the anti-addiction medicine naltrexone reduces drinking in alcohol-dependent patients within two days of being injected, according to a new study.

Naltrexone blocks opioid receptors and is approved for use in alcohol-dependent patients. To improve adherence, "an intramuscular, injectable, extended-release formulation of naltrexone has been developed," Dr. Domenic A. Ciraulo, of Boston University School of Medicine, and colleagues explain in the Journal of Clinical Psychiatry. The researchers tested injectable naltrexone XR in some 600 actively drinking, alcohol-dependent men and women who were given one of two doses of the drug or an inactive placebo every four weeks for 24 weeks. The participants also received 12 sessions of standardised, low-intensity psychosocial therapy.

Compared with the placebo patients, patients given the higher dose of naltrexone had a significant reduction in the average daily number of drinks consumed by the second day.