IS the length of the clinical trial very long? Why?

Unlike engineering, medical field always goes for top down approach. The total aspects regarding the health of the human being are being examined before the treatment is given. A wrong treatment cannot take human health as an excuse. Any medicine undergoes a detailed research for years before it comes out in the market and the clinical trial in fact, is the last stage of the research. The medicine for treating the diseases like cancer took almost 8 years to pass the clinical trial. Availability of participants, researchers, seasonal variations and effectiveness of the medicine are few reasons for the time lag in the clinical trials.   

Clinical trials demand the inclusion of participants that are suffering from certain diseases. Finding the eligible list and obtaining their consent is not always easy. The efficient researchers have to invest good amount of time in bringing out the medicine or treatment and availability of researchers and their willingness to drive their efforts into the clinical trial is the another problem. Clinical trial for certain diseases like allergies and seasonal born disorders has to be conducted during particular time period of the season.  Apart from that, budgetary constraint in the long run clinical trial is always a problem unless you have right sponsor or right budgetary plan.