Clinical trials help us discover new treatments. Learn more about how clinical trials work.
You may have heard about clinical trials — studies of possible new treatments or medications — but wonder what exactly they are and if one might be right for you. Deciding whether to participate in a clinical trial can be a complex decision. In order to make that decision, it may help you to know more about what clinical trials are and how new treatments are studied and approved for wider use.
What are clinical trials?
Clinical trials are used to test new forms of therapy. Clinical trials are used to evaluate potential treatments that have had some positive effect against disease in the test tube, in animal experiments or in a limited number of people. Therapies tested in clinical trials may not yet be established treatments. Clinical trials may test new treatment, including new drugs, surgical procedures, medical devices such as pacemakers or stents, radiation therapy, or novel approaches to treatment, such as gene therapy.
Clinical trials may compare two commonly used, standard therapies to see if one is better than the other. Clinical trials may also compare a group of people who get the experimental treatment with another group who gets an inactive substance, known as a placebo. Any difference between groups or treatments can thus be attributed to the experimental treatment.
All research should begin with a basic ethical question: "Do the potential benefits outweigh the potential harm?" Researchers design trials that allow them to learn as much as possible about a new treatment or medication in ways that minimize the risk of injury to participants.
The goal of clinical trials is to determine if a treatment both works and is safe. Therapies that prove effective during trials may become new treatment options. Because research trials are primarily geared toward benefiting future patients with a particular illness, those who take part in the earliest studies of a treatment may not personally benefit from the treatment being tested. However, new therapies may potentially be effective for study participants.
Who can participate in clinical studies?
Anyone can participate in a clinical trial if they meet the criteria of that trial. Researchers are usually looking for people with the condition that the medication is meant to treat. But some trials need healthy people to investigate ways to prevent disease from happening or to determine side effects and effective doses of certain medicines.
Many people take part in a clinical trial because treatments for their condition aren't available. If standard treatments haven't worked, you might consider a clinical trial as an option. Some people join clinical trials mainly to help people who might develop the same condition in the future.
Also important is whether you've been treated for your condition. If an effective treatment for your condition exists, then you aren't likely to be eligible to participate in a clinical trial — you may become eligible if the standard treatment no longer works for you. Some studies are restricted to people who haven't started treatment, while others focus on people who've unsuccessfully tried other options first.
Each trial has a list of criteria for who can participate, including age, sex, and type of disease and its progression. In order to ensure the treatment is safe for everyone who might take it, clinical trials ideally need to include people of many races and of both sexes.
How much will you know about the treatment being investigated?
It's crucial that you have enough information about the study and the treatment being investigated to make a well-informed decision. To do this, the study facilitators provide what's called an informed consent document. You must read this and then sign an informed consent form before being allowed into the trial. This informed consent document contains information you'll need to know about the study before deciding whether to participate. Some of the information on an informed consent document includes:
- What will happen during the clinical trial, including tests you may be given
- Known risks and benefits of the experimental treatment
- How long you'll be expected to participate in the clinical trial
- Other treatments that might be helpful to you instead of the treatment being tested
- Who to contact with questions
The form must explain this information in words you can understand. Researchers aren't allowed to pressure you into signing up for a trial if you prefer not to get involved. Signing the informed consent form means you agree to participate in the trial as explained by the researcher and described on the consent form. If you later decide to leave the study, you may do so without any penalty at any time.
In the case of children, the trial participant may not be required to sign an informed consent form. If the participant is a young child, the parent or legal guardian must give informed permission, and the child must agree to enter the study. If the child is unable to agree — for example, if the child is an infant — a parent or legal guardian may give consent instead.
What types of clinical trials are available?
Before any treatment is tested in people, it must be proved safe and effective in the laboratory or in animals — sometimes called preclinical research. This usually takes one to three years. When a treatment is tested in people, it always takes place in distinct phases. Each phase has a different purpose. Treatments being tested must go through the testing phases in order, including:
Phase I research
This is the first step in testing in humans. At this stage researchers study:
- How much of the treatment to give
- How the human body reacts to the treatment
- How much can be given safely
- The best way to give the treatment
- Any harmful effects
Earlier studies have often only been done in animals, so the approach may pose some risks when first tried in humans. Researchers try to minimize these risks by starting with very small doses, and then increasing the dosage only if no or minimal side effects occur. Only a limited number of people who would not be helped by existing treatments are included in these trials. Between 20 and 80 volunteers typically participate in Phase I studies, which usually last several months. About 70 percent of the drugs tested in Phase I are successful and move on to the second phase of research.
Phase II research
This phase focuses on determining whether a new approach works the way it's intended. For example, does it shrink a tumor? Researchers also monitor you for common short-term side effects that occur with the therapy. Some things aren't yet known about the treatment, so risks are still present. Several hundred people may participate in these studies, which can last from several months to years. On average, a third of the drugs tested in Phase II are successful and move on to the third phase of research.
Some clinical trials may compare a potential new treatment with a placebo — a pill or liquid that looks like the new treatment, but has no active ingredients. Before you participate in any trial, you'll be told whether a placebo will be involved. If you agree to participate, you must be willing to take a chance that you'll get the placebo and not the active treatment. Neither you nor your doctor can control which you will receive.
Phase III research
This phase usually begins only after a treatment shows promise in phases I and II. At this stage, you're often assigned randomly to receive either the experimental treatment or the standard treatment. This helps to avoid bias in the results.
Phase III trials provide more information about the safety of the experimental treatment and demonstrate whether the standard or the experimental treatment group has better survival rates and fewer side effects. These trials usually include several hundred to several thousand people and last from one to four years. Large trials make it easier to estimate what would happen if the experimental treatment were available to everyone with the condition. About 25 percent to 30 percent of drugs tested in Phase III are successful and go on to the government for approval.
Phases of clinical studies
| Phase | Number of participants | Length of study | What researchers are studying | Success rate |
| Phase I | 20-80 | Several months | Safety | 70 percent |
| Phase II | 100-300 | As long as two years | Effectiveness | 33 percent |
| Phase III | 1,000-3,000 | One-four years | Safety, effectiveness and proper dosage | 25-30 percent |
Source: National Institutes of Health, 2005, and the FDA Center for Drug Evaluation and Research, 1999
What happens after a clinical trial is over?
After a phase I or II trial, researchers decide whether to move on to the next phase or stop testing. When a phase III trial is complete, researchers decide whether the results show enough medical importance. Depending on the outcome of those evaluations, the researchers may try and get the results published in a peer-reviewed, scientific journal. Peer review means other medical experts review the trial to make sure the results are sound.
If the results are promising, the researchers or company they work for may submit an application to the Food and Drug Administration (FDA) asking permission to make the experimental treatment available to the public.
On average the approval process takes about a year, but it can take several more. Some drugs are approved in a matter of months. These drugs are considered priority drugs — drugs that provide a significant advance in treatment for a life-threatening condition. The FDA's goal is to rule on these drugs no more than six months after they've been submitted for approval.
Sometimes research continues even after a treatment is approved for wide use. This research, called Phase IV research, tracks what happens to people who use an experimental treatment after the FDA has approved it. In these trials, the investigators record the side effects and results occurring in people who undergo a treatment or take a drug. Phase IV studies usually don't include a control group because the treatment has already been approved.
Phase IV trials aren't required for every treatment that's approved. In some cases, the FDA may require that a manufacturer perform the studies when the agency wants to be sure that there are no other side effects or that the known side effects aren't too serious. Sometimes companies launch Phase IV studies with the hope of collecting data that show their product is better than a competitor's product.
Last Updated: 07/02/2007
