The prevalence of Erectile Dysfunction [ED] for men aged 40 is estimated at 2%, 25-30% for men aged 65, and greater than 50% for men over age 75. Even greater numbers of patients with ED are projected for the future as awareness of both the disorder and viagra grows among patients and physicians. This, combined with the maturing boomer generation, suggests that the market will be quite large.
During the first year out, many will try it at least once. While it is not a chronic drug, the first time users will fuel sales for a while. For example, the nicotine patch sold about $800M the first year, and sales fell later as its limitations became clear. Viagra should have a big first year or so of sales regardless of how often it is used.
It may also sell in unintended markets. Questions as to how it effects performance of the under 40 set is not clear. If it allowed a greater frequency or more rapid recovery of erectile capabilities during repeated romantic interludes, it could find a large nitch there, too. I think the market size will actually surprise many of us.
Pfizer definately rates a buy for the next 6 mos. or so.