A chemical in cocoa could soon be turned into a medicine for persistent cough, researchers claim. Scientists are carrying out the final stages of clinical trials of a drug that contains theobromine, an ingredient found in chocolate and cocoa.The UK developers say the drug could be on the market within two years. Every year in Britain an estimated 7.5m people suffer from persistent cough - a cough lasting more than two weeks. Most current medicines used to control the symptoms are opiate-based ones like cough syrups containing codeine, a narcotic. Agencies