FRANKFURT, Sept. 6 - The year's big drug-industry merger may turn out to be about using marketing muscle to fight fat. In April, when the French drug company Sanofi-Synthélabo vanquished all other players with a long-shot takeover bid for a much larger French-German rival, Aventis, many commentators focused on the role of politicians in Paris. The French government, determined to create a national champion in pharmaceuticals, all but stage-managed the deal, which created the world's third-largest drug company, after Pfizer of the United States and GlaxoSmithKline of Britain. But last week, with Sanofi's release of promising test results for a...