Enlarge Image A needle a day. Inserting needles into certain acupuncture points, shown here as labeled dots, seems to spur tissue to release a pain-killing chemical. Credit: Takahiro Takano Millions of people worldwide use acupuncture to ease a variety of painful conditions, but it's still not clear how the ancient treatment works. Now a new study of mice shows that insertion of an acupuncture needle activates nearby pain-suppressing receptors. What's more, a compound that boosts the response of those receptors increases pain relief—a finding that could one day lead to drugs that enhance the effectiveness of acupuncture in people....