Drugs are packaged at the Stada Arzneimittel factory in Bad Vilbel, Germany. Photographer: Krisztian Bocsi/Bloomberg Stada Arzneimittel AG is about as unexciting as a company can be. Based in a sleepy spa town just outside Frankfurt, the drugmaker makes Snup nose spray, Grippostad cold pills, and other branded drugs for common ailments, as well as low-cost copies of medications such as cholesterol drug Lipitor and pain balm Voltaren. Founded in 1895 as a pharmacists’ cooperative, Stada was long sheltered by restrictions making it complicated to sell shares—an ownership structure that ensured stability and made the company a difficult acquisition target....