Contrary to promising earlier reports, an orally administered preparation of the antiviral drug pleconaril only appeared to reduce the duration of the common cold slightly when compared to a placebo; for example, in Caucasian patients who were not taking other cold medications at the time, pleconaril reduced the average duration of symptoms from 9 days to 6.75 days. It had no significant effect in African Americans.  In a separate study, the drug was ineffective in managing viral meningitis in children.

There were also safety concerns since a study of the use of the drug in prophylaxis for picornavirus respiratory infections  revealed increased menstrual irregularities. There is a possibility that pleconaril might increase the metabolism of some oral contraceptives and reduce their efficacy. Pleconaril might also interfere with drugs used to treat HIV. Thus, it would seem that the risks outweigh the modest reduction in symptoms. Moreover, the use of a single agent might encourage the emergence of resistant and possibly more pathogenic enteroviruses in the community.