Drug Approval Process

Eligibility – who can take part in clinical trials?

The guidelines determining who can take part in clinical trials are called eligibility criteria. These criteria are designed to ensure that the type of patients most likely to benefit from the new drug take part in the trial and to reduce the chance that participants are put at risk. Sometimes researchers conduct early trials in a group of patients who are relatively similar, so that the outcomes can be reliably compared. If the results are encouraging, later trials may include a more varied patient population.

Inclusion criteria

Inclusion criteria state who may participate in a clinical trial. They may include a list of characteristics such as age, gender, diagnosis or disease stage.

Exclusion criteria

Exclusion criteria state who may not participate in a clinical trial. For example, people who have taken a particular drug prior to the trial may be excluded. Pregnant women are often excluded from clinical trials because there is usually insufficient information available on possible risks the new drug may pose to the unborn baby.

Risks and benefits

The researchers who design clinical trials take great care to maximize the chances of benefits and to reduce the risks to participants. Investigational drugs are always tested in the laboratory and in animals before they are tested in humans. Nevertheless, they may cause unexpected, unpleasant side effects. Before the trial starts, the researchers inform participants about any side effects that they know about, such as those that patients in earlier phase trials have experienced. All participants are monitored very carefully throughout the trial and sometimes also after the trial is completed. This enables the researchers to quickly identify any side effects and to take action to minimize them.

There may be some inconvenience to participants, including the need to visit the trial center regularly, to fill in questionnaires, keep a symptom diary or undergo extensive interviews and physical examination. Travel costs can usually be reimbursed.

While benefits cannot be guaranteed, advantages of participating in clinical trials could include gaining access to potentially beneficial new drugs before they are widely available. In addition, patients may benefit from the extra medical attention as any changes in health status are picked up and acted on early. They may also feel empowered by the knowledge that they are taking an active role in their own health care and helping other patients by participating in the development of new treatments.

Some clinical trial terminology


Each clinical trial is conducted according to a detailed study plan called a protocol. This is carefully designed by the researchers to ensure that the participants’ health is safeguarded and that the trial will yield answers to specific research questions. The protocol includes the eligibility criteria, the proposed dosing and testing schedule and the trial duration.

Randomized Controlled Trial (RCT)

Participants in RCTs are randomly assigned to one of two or more groups at the start of the trial. One group is given the trial drug and the other group is given an inactive treatment (placebo), an alternative treatment or no treatment. The group receiving the trial drug is called the experimental group and the other group is called the control group. Researchers follow both groups to compare the outcomes.


A placebo is a pill, or injection with no treatment value (a “sugar pill”). It is given to patients in the control group of a controlled clinical trial. The placebo should have the same appearance as the active drug received by the experimental group, and should be administered in the same manner and with the same schedule.

Double blind

In double blind trials neither the participants nor the researchers know who is receiving the trial drug and who is receiving a placebo. An independent third party codes the trial drug and the placebo materials and holds the code secretly until the study is completed or a significant adverse effect requires ‘unblinding’ where participants and researchers are informed as to which participants received the investigational drug or the placebo.

Open label

Participants and researchers all know what drug and what dose is being received.


Multi-center trials include patients and researchers in a number of different locations, often from different countries all around the world.

Informed consent

Before trials start, researchers are legally required to explain all the important information about the study to the participant. They must ensure that the participant understands the risks and benefits, that enrollment is voluntary and that if the trial is placebo controlled, they may not receive the active treatment. Once the participant agrees to participate in the study they would then sign an informed consent form.