Examples

Viagra

Viagra is a FDA approved pill. It is used to treat erectile dysfunction. However it initially was produced to treat Hypertension, which is high blood pressure. During it's initial clinical trial several things may have been noticed: one, it may have been noticed that Viagra was not showing any additional factors that would make it better than the current treatment for hypertension two, in some males they experienced an erect penis as an adverse side effect. Because those who were used in the study were not looked at on whether or not they had erectile dysfunction, the company had an important decision to make about the fate of the pill. 

The decision made was to test Viagra and see how well it would treat males with erectile dysfunction. Because the market for erectile dysfunction was relatively unknown because of it's nature of privacy. Before Viagra males with this disorder could result to therapy, and or penile implants. However the pill provided a probably cheaper less painful way to treat their disorder. It has been seen through the last several years that Viagra has gained much momentum, and is a very hot topic of discussion. Now after its patent has expired, there are others who like Viagra treat erectile dysfunction. Had the company decided against the clinical trial for Viagra they might have lost a lot of money in what has become a very lucrative market. 

Now, the makers of Viagra are conducting even more clinical trials (Phase III) on a smaller dose of the active ingredient in Viagra, sildenafil citrate. They claim that smaller doses of the active ingredient are actually better at treating hypertension.

With Viagra it is very easy to see the importance of clinical trials. Had it not been for clinical trials, Viagra may not have been noticed to treat erectile dysfunction. And now with a smaller dosage in trial, which is technically Phase IV for Viagra, and Phase III for the new smaller dosage of Viagra, they have the opportunity to tap into a different market and hopefully help the lives of many whom suffer from Hypertension. 

Phen-Fen

Phen-Fen was also a FDA approved product. It was used to treat obesity, however during it's Phase IV adverse reactions were observed. Approximately 3 people died, and 40-50 were seriously injured. Those who were injured all suffer from some sort of leaky valve of the heart. The longer the patient took the pill, the more severe the damage was. 

In this case, the Trials themselves has failed. Due to small group size, under representation of all groups, and short approval and trial time the pill was not noticed to cause any adverse reactions. During it's Phase IV patients who took the pill during trial and those who are taking it after it was released to market were still being watched by doctors. Any problems that a doctor noticed that was due to the medicine was reported to Manufacturing company which then let the FDA know of the unseen reactions, which resulted in the removal of Phen-Fen from the market after approximately four months.