Naloxone induces miosis in normal subjects

In a placebo-controlled trial, pupillary constriction was measured in healthy non-addicted subjects and in opiate addicts by using static computer-assisted pupillometry. In contrast to earlier reports, a clear-cut pupillary constriction was observed in healthy persons after a single intravenous injection of 0.4 mg naloxone. No significant changes of pupillary size were recorded in the same subjects after the administration of a placebo. In methadone-maintained subjects, the IV administration of 0.4 mg naloxone caused a significant pupillary dilatation. From these data it can be concluded that naloxone seems to have a central pharmacological action not only in opiate addicts, but also in healthy persons. This is demonstrable by studying the miotic response.