Less morphine may be more
In mice, very low doses of morphine combined with even lower doses of a drug that usually blocks morphine’s effect can give greater pain relief than higher doses of morphine alone, according to a report in the January Brain Research.
Researchers tested pain sensitivity by measuring how long mice let their tails remain in a hot-water bath. Stanley M. Crain and his colleagues at the Albert Einstein College of Medicine in New York showed that very low doses of morphine–one-tenth to one-hundredth the normal dose–made mice more sensitive to pain than a mouse getting no morphine. These results confirmed their earlier findings showing that low doses of morphine increase the excitability of pain-related nerve cells.