In health care, including medicine, a clinical trial (synonyms: clinical studies, research protocols, medical research) is the application of the scientific method to human health. Observational studies are those in which individuals are observed and their outcomes are measured by the investigators (e.g., natural experiment). Interventional studies are those in which the research subjects are assigned by the investigator to a treatment or other intervention, and their outcomes are measured. Researchers use interventional clinical trials to test hypotheses about the effect of a particular intervention upon a pathological disease condition. Well-run clinical trials use defined techniques and rigorous definitions to answer the researchers' questions as accurately as possible.
Clinical trials are only a small part of the research that goes into developing a new treatment. Potential drugs, for example, first have to be discovered, purified, characterized, and tested in labs (in cell and animal studies) before ever reaching clinical trials. In all, about 1,000 potential drugs are tested before just one reaches the point of being tested in a clinical trial. On average, a new cancer drug has at least 6 years of research behind it before it even makes it to clinical trials. But the major holdup in making new cancer drugs available is the time it takes to complete clinical trials themselves. On average, about 8 years pass from the time a cancer drug enters clinical trials until it is approved.
Why so long? To establish safety and effectiveness, researchers look at each new treatment in several different studies. Only certain people are eligible to take part in each clinical trial. And cancer trials, by their very nature, take years to complete. It takes months, if not years, to see if a cancer treatment works in any one person.
The biggest barrier to completing studies is the shortage of people who take part. Fewer than 5% of adults with cancer will do so. According to the Pharmaceutical Research and Manufacturers of America (PhRMA), about 400 cancer medicines were being tested in clinical trials in 2005. Not all of these will prove to be useful, but those that are may be delayed in getting approved because the number of participants is so low.
The most commonly performed clinical trials evaluate new drugs, medical devices, biologics, psychological therapies, or other interventions on patients in strictly scientifically controlled settings, and may be required for regulatory authority approval of new therapies. Trials may be designed to assess the safety and efficacy of an experimental therapy, to assess whether the new intervention is better than standard therapy, or to compare the efficacy of two standard or marketed interventions. The trial objectives and design are usually documented in a clinical trial protocol.
