What are the different types of clinical trials? 
Treatment trials - test experimental treatments, new combinations of drugs, or new approaches to surgery or radiation therapy.
Prevention trials - look for better ways to prevent disease in people who have never had the disease or to prevent a disease from returning. These approaches may include medicines, vitamins, vaccines, minerals, or lifestyle changes.
Diagnostic trials - are conducted to find better tests or procedures for diagnosing a particular disease or condition.
Screening trials - test the best way to detect certain diseases or health conditions.
Quality of Life trials - (or Supportive Care trials) explore ways to improve comfort and the quality of life for individuals with a chronic illness.
What are the phases of clinical trials? Clinical trials are conducted in phases. The trials at each phase have a different purpose and help scientists answer different questions:
In phase I trials, researchers test an experimental drug or treatment in a small group of people (approximately 20-80) for the first time to evaluate its safety, determine a safe dosage range, and identify side effects. It is designed to find out if the drug is safe rather than whether the drug is effective. Phase I is also used to learn what drug doses to use in later trials, how the drug is broken down in the body and excreted, and study short-term side effects.
In phase II trials, the experimental study drug or treatment is given to a larger group of people (approximately 100-300) to see if it is effective and to further evaluate its safety.
In phase III trials, the experimental study drug or treatment is given to large groups of people (approximately 1,000-3,000) to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the experimental drug or treatment to be used safely. These are most often the clinical trials that make headlines. These are large-scale tests with hundreds or thousands of patients. They are the culmination of earlier phase I and phase II trials that include many fewer people and still earlier pre-clinical experiments with animals. They are also the final tests in humans before the FDA is asked to authorize sale of new medicines or devices.
Types of Phase III Trials:
1. Randomized, Double Blind - Randomized means people are assigned at random (by chance) either to receive the new drug, device or treatment or the standard treatment for that disease, or a nonfunctional substitute (such as a sugar pill). This last group is often called the control group, or the placebo group. Because phase III must answer definitively whether the investigational product works, it's important to compare people who receive it with others who do not. A double-blind or double-masked study is one in which neither the participants nor the study staff know which participants are receiving the experimental treatment and which ones are receiving either a standard treatment or a placebo. These studies are performed so that neither the patients’ nor the doctors’ expectations about the experimental treatment can influence the outcome.
2. Open trials - Not every trial is blind. In unblinded trials, often described as open trials, both doctors and participants know what treatments are being given. Trials of surgical procedures and comparisons of medical devices are often by nature open. One of the problems with an open trial is that many participants may not want to take placebos, because they presume the investigational treatment will be better. Open trials, like single-blind trials, are considered to be more prone to error than double-blind procedures.
3. Factorial trials - When patients are being treated with a combination of drugs, as is current practice for HIV infection, a new drug may be evaluated by testing it in combination with other drugs rather than by itself. A factorial design trial may be used for this purpose. A simple factorial design would have one group testing therapy A, another testing therapy B, a third group testing A and B combined, and a control group testing neither A nor B. Factorial designs are considered an efficient way to test medicines in combination, but their results are not always easy to interpret.
4. Crossover trials - In a crossover trial, each participant gets both treatments being tested. Some participants are assigned at random to receive treatment A, and later, treatment B. Others receive B, then A. To produce valid results, the effect of the first treatment must end before the second treatment is taken, and vice-versa. This requirement can be hard to satisfy, and is one reason crossover trials are not often used.
5. Orphan Drug trials - Orphan drug trials test drugs designed to treat diseases affecting fewer than 200,000 Americans. Some are rare genetic diseases that occur when missing or defective enzymes prevent essential biochemical reactions from happening. Because affected individuals are so few, an orphan drug may be tested only on a small number of participants, who generally are so sick that if the drug works, their improved health is readily apparent.
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phase IV trials, post marketing studies delineate additional information including the investigational product’s risks, benefits, and optimal use.