Overview

Trials of drugs

Some clinical trials involve healthy subjects with no pre-existing medical conditions. Other clinical trials pertain to patients with specific health conditions who are willing to try an experimental treatment.
When participants are healthy volunteers who receive financial incentives, the goals are different than when the participants are sick. During dosing periods, study subjects typically remain under supervision for one to 40 nights.
Usually pilot experiments are conducted to gain insights for design of the clinical trial to follow.
There are two goals to testing medical treatments: to learn whether they work well enough, called "efficacy" or "effectiveness"; and to learn whether they are safe enough, called "safety". Neither is an absolute criterion; both safety and efficacy are evaluated relative to how the treatment is intended to be used, what other treatments are available, and the severity of the disease or condition. The benefits must outweigh the risks.^[3][4]:8 For example, many drugs to treat cancer have severe side effects that would not be acceptable for an over-the-counter pain medication, yet the cancer drugs have been approved since they are used under a physician's care, and are used for a life-threatening condition.^[5]
In the US, the elderly constitute only 14 percent of the population, while they consume over one-third of drugs.^[6] People over 55 (or a similar cutoff age) are often excluded from trials because their greater health issues and drug use complicate data interpretation, and because they have different physiological capacity than younger people. Women, children and people with unrelated medical conditions are also frequently excluded.^[7] For women, a major reason for exclusion is the possibility of pregnancy and the unknown risks to the fetus.
The sponsor designs the trial in coordination with a panel of expert clinical investigators, including what alternative and/or existing treatments to compare to the new drug and what type(s) of patients might benefit. If the sponsor cannot obtain enough test subjects at one location investigators at other locations are recruited to join the study.
During the trial, investigators recruit subjects with the predetermined characteristics, administer the treatment(s) and collect data on the subjects' health for a defined time period. Data include measurements such as vital signs, concentration of the study drug in the blood and/or tissues, changes to symptoms, and whether improvement or worsening of the condition targeted by the study drug occurs. The researchers send the data to the trial sponsor, who then analyzes the pooled data using statistical tests.
Examples of clinical trial goals include assessing the safety and relative effectiveness of a medication or device:

• On a specific kind of patient, for example, a patient who has been diagnosed with Alzheimer's disease
• At varying dosages, for example, a 10 milligram dose instead of a 5 milligram dose
• For a new indication
• Evaluation for improved efficacy in treating a patient's condition as compared to the standard therapy for that condition
• Evaluation of the study drug or device relative to two or more already approved/common interventions for that condition, for example, device A versus device B, or therapy A versus therapy B)

While most clinical trials test one alternative to the novel intervention, some expand to three or four and may include a placebo.
Except for small, single-location trials, the design and objectives are specified in a document called a clinical trial protocol. The protocol is the trial's "operating manual" and ensures that all researchers perform the trial in the same way on similar subjects and that the data is comparable across all subjects.
As a trial is designed to test hypotheses and rigorously monitor and assess outcomes, it can be seen as an application of the scientific method, specifically the experimental step.
The most common clinical trials evaluate new pharmaceutical products, medical devices (such as a new catheter), biologics, psychological therapies, or other interventions. Clinical trials may be required before a national regulatory authority^[8] approves marketing of the innovation.

Trials of devices

Similarly to drugs, medical devices are sometimes subjected to clinical trials. Device trials may compare a new device to an established therapy, or may compare similar devices to each other. An example of the former in the field of vascular surgery is the Open versus Endovascular Repair (OVER trial) for the treatment of abdominal aortic aneurysm, which compared the older open aortic repair technique to the newer endovascular aneurysm repair device.^[9] An example of the latter is the LEOPARD trial, which compares EVAR devices.^[10]

Trials of procedures

Similarly to drugs, medical or surgical procedures may be subjected to clinical trials,^[11] such as case-controlled studies for surgical interventions.^[12]