Clinical testing is complex and time-consuming, averaging 14 years to complete Phase I through III testing to gain FDA approval. Sometimes, drugs will fail in clinical tests because the animal tests did not accurately predict their effects in humans. Often people wonder why it takes so long to develop a new drug and why sometimes a drug treatment (like fen-phen, which may cause heart valve damage) is not found to be dangerous until after it is sold to the public. Think about all the different possibilities that need to be explored, such as:
Does the drug cause a dangerous reaction when mixed with any other prescription or over-the-counter drug?
Is the drug safe for pregnant women, children, and the elderly and at what dosage?
Does the drug cause birth defects or subtle learning disabilities that may not be discovered until a child is in school?
Does the drug cause cancer, which may take 20 years to develop?
Is there a small number of patients who are genetically more susceptible than average to side effects?