Pfizer stock has dropped 50% over the past three years.A few years ago, Pfizer (PFE +1.48%) represented the ideal pharmaceutical stock investment. The company, as leader in the coronavirus vaccine and treatment market, offered a great deal of growth, and thanks to its broad variety of products across indications and its commitment to dividend payments, offered investors safety too.But in more recent times, the pharmaceutical giant has experienced its share of struggles. Demand for coronavirus vaccines and t ...