Understanding Clinical Trials



Table of Contents

What Are Clinical Trials?

The term clinical trial is used to describe many different types of research studies. There are five main types of clinical trials:

  • Treatment trials
    Study new medications, new combinations of existing medications, or new types of therapies
  • Prevention trials
    Look for better ways to prevent disease—sometimes with medicines, sometimes with behavior changes
  • Diagnostic trials
    Test the best way to detect disease or changes within the body
  • Natural History trials
    Study the natural progression of disease in the human body
  • Quality of Life trials
    Study ways to improve aspects of life for people living with illnesses

The Basic Components of Clinical Trials

The scientists and health care providers who manage clinical trials are usually called investigators. The people who join clinical trials are usually called participants, but may be referred to as volunteers or study subjects. ALL clinical trials are voluntary – you never have to participate in a clinical trial unless you want to.

Each clinical trial has a written plan, or study protocol, that describes the goals of the study, how long the study will last, which people are eligible to participate (also called inclusion and exclusion criteria), and what tests and procedures are required of each participant.

Inclusion and exclusion criteria are the guidelines used to determine who can and cannot participate in a specific clinical trial. Inclusion criteria are requirements that a person must meet to participate (such as CD4 cell count, viral load, or age). Exclusion criteria are factors that prevent a person from participating either for his or her safety or to make it easier to understand the study results. For example, people might be excluded for having liver problems, or if they have already used a drug that is being studied.

Each participant in a clinical trial must sign an informed consent. When you sign this document it means that you understand the details of the study and you agree to participate. You may also want to take the document with you and talk about the study with your health care provider, family, or friends before you decide to participate. If your native language is not the language spoken by the people describing the study, you may ask if translation is available. It is important that you truly understand the study and what you will be asked to do. If you have any questions, be sure to ask the study staff. It is their job to make sure that, when you sign, you are making an informed choice.

You may be paid for travel expenses to and from the study site and for your time. Childcare may also be provided. You can choose to drop out of a study at any point and for any reason.

The Stages of Treatment Trials

The most common type of clinical trial in HIV is a treatment or drug study. There are four stages, or phases, of clinical trials for new treatments. With each phase, a little more is known about the treatment being studied. Each phase has a different purpose and helps researchers answer specific questions about the drug in trial.

  • Phase I: Is the drug safe?
    A Phase I trial tests a drug in a small number of participants (usually fewer than 80) to find a safe dose and to record the side effects of the drug. Phase I trials usually last a few days to a few weeks.
  • Phase II: Is the drug effective?
    A Phase II trial tests a drug in a larger number of participants (on average 100 to 300) to see if the drug works. Phase II trials may also test different doses of the drug to find which dose works best. The safety of the drug also continues to be evaluated. A Phase II trial usually lasts six months to one year.
  • Phase III: Is the drug safe and effective in larger groups of people for longer periods of time?
    A Phase III trial tests a drug in a very large group of participants (typically 1,000 to 3,000). Phase III trials gather more information about the safety and effectiveness of the drug by comparing it to an existing medication. Phase III trials generally last two to three years.
  • Phase IV or Post-Marketing studies:
    What are the long-term results of using the drug? These trials are done after US Food and Drug Administration (FDA) approval to get more information about the drug's best use and to further examine long-term side effects.

Once a drug trial has completed the first three phases of research, the company that makes the drug submits the study data to the FDA for approval. Because the need for treatments for HIV is so great, a drug company can apply for something called accelerated approval if its drug offers something new or meets a need for people living with HIV (HIV+).

Accelerated approval happens faster than regular drug approval and it may put special restrictions on how the drug can be used. However, even if a drug gets accelerated approval, the drug company must continue doing long-term research on the drug for it to get full approval.

Should I Participate in a Clinical Trial?

Choosing to participate in a clinical trial is a big decision. There are risks and benefits to consider when making the choice.


  • You may experience unpleasant or serious side effects
  • You may have to stop all current medications, including any HIV medications
  • You may receive a placebo (sugar pill)
  • There is no guarantee that the experimental drug will be an effective treatment for you


  • You may experience health benefits from a new treatment that is not yet available to the general public
  • Most trials provide free laboratory tests and expert care for the purpose of the study
  • You are contributing to the development of a new medication or increasing understanding of HIV disease

Clinical Trials and HIV+ Women

Worldwide, women represent over half of all those living with HIV. In the past, women were excluded from participating in many types of clinical trials. Now, despite being able to participate freely, the FDA reports that women represent only one in every five study participants.

It is important to participate in research because HIV and some of the HIV drugs act differently in women's bodies. More information is needed on correct drug doses for women, differences in lab tests such as CD4 cells and viral load, how opportunistic infections and gynecologic conditions affect HIV+ women, and what side effects are likely to affect women. The only way to find out this information is for more HIV+ women like you to join clinical trials. For information on a clinical drug trial in the US that was successful in recruiting large numbers of women and people in color, see The Well Project's article, Lessons from GRACE.

Additional Resources

Select the links below for additional material related to clinical trials.

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