Opium poppies, such as the Tasmanian poppies pictured here, are prized for the valuable drugs they produce. Scientists have long known how the plants make opiates, such as codeine and morphine, but the molecular steps for making a nonaddictive substance called noscapine have been a mystery until now. Noscapine is a cough suppressant that is also used as an antitumor drug. A group of 10 genes carries the instructions for building enzymes Papaver somniferum poppies need to produce noscapine, Ian Graham of the University of York in England and colleagues report online May 31 in Science. Poppies with two copies of each of the noscapine-producing genes make high levels of the drug, while poppies that inherit only one copy of the genes make less noscapine. Poppies that lack the genes make none of the drug. The discovery could make it easier for drug companies to manufacture noscapine.