Understanding Clinical Trials

what are clinical trials?

Clinical trials are research studies that involve people. These trials test whether a new treatment, like a drug, cell therapy, gene therapy, or surgery, is safe and effective.

Clinical trials are one of the last steps in the research process. Researchers work for years to understand the treatment in the lab and animal models before a clinical trial starts. It can take 12-15 years from the beginning of the research process to the sale of a new drug or treatment. The cost for this process can cost between $500 Million to $2 Billion.

When you take part in a clinical trial, you are contributing to the progress of research. You are helping researchers find out if the treatment is helpful, harmful, or no different than an alternative. You may experience positive effects from the study treatment before it is available on the market. However, it is important to remember if you choose to take part in a trial that:

  • You are not guaranteed to receive the treatment. In some trials up to half of participants may receive a placebo, or sham treatment.
  • If you receive the treatment, there is no guarantee that it will work.
  • You may experience side effects; some may be serious.


  • Sponsor: the company or institution that is responsible for managing and funding the clinical trial.
  • Investigators: the scientists and doctors who manage the clinical trial. The Principal Investigator is the person in charge of the trial.
  • Study Protocol: study protocol is the plan for the trial. The protocol includes the goal, time, type of people who can participate (see below), and what tests will be used.
  • Outcome: an outcome is something that is measured during the trial to determine if the treatment is working and is safe. Some examples of outcomes are the number and seriousness of side effects, improvement in vision or ability to navigate through a maze.
  • Inclusion criteria: the traits a person must have to participate in a trial. For example, a clinical trial testing a gene therapy for the USH2A gene might have in its inclusion criteria “must have genetically confirmed USH2A gene mutation.”
  • Exclusion criteria: anything that could prevent someone from participating in a trial. The reason for exclusions is to keep you safe or to make it easier to understand the results. For example, some trials exclude people with multiple eye diseases.
  • Informed consent: informed consent means you understand the details of the study and you agree to take part. Before you take part in a clinical trial, the coordinator will go over all the details of the trial with you. You will be able to ask questions, express concerns or choose not to take part. If you choose to take part, you will sign a document called informed consent. You will always have the chance to ask questions during the trial. You also have the chance to leave the trial at any time.
  • Compensation: The Sponsor will normally pay for costs associated with clinical trial participation, such as travel and hotel.

types and phases of clinical trials


A natural history study follows a group of people with a specific disease or gene mutation over time. There is no treatment provided during this study. The purpose of a natural history study is to collect information about how the disease develops and progresses. This information is collected using clinical tests, doctor’s reports, and patient reported symptoms. Natural history studies are important because they provide more information about diseases, especially rare diseases. These studies inform development of new treatments and clinical trial design.


This is the first time a treatment (also called an intervention) is given to a human. A Phase 1 trial tests the treatment in a small group of participants. The purpose of a Phase 1 trial is to test if the treatment is safe, find a safe dose and measure side effects.


If a Phase 1 study shows that a treatment is safe, scientists can launch a Phase two trial. In Phase two trials, a larger group of participants receive the treatment. Phase 2 trials look at how effective a treatment is at different dose levels, while continuing to measure safety. Sometimes Phase 1 and Phase 2 trials are combined to speed up the process.


In Phase 3, the trial measures safety and effectiveness in a larger group of patients at different stages of disease. The new treatment is compared to current treatments or a placebo. A placebo is a fake intervention, such as a sugar pill. Phase 3 trials are often double-blind, meaning neither the participants nor investigators know which person is receiving treatment or placebo. If the results of a Phase 3 trial are successful, the company can then apply to have their treatment approved for sale. Read more about this process on

phase 4: long term follow up

Phase 4 trials takes place after an intervention has been approved for sale and is being used as treatment. Investigators aim to learn more about the long-term outcomes and to monitor side effects of the treatment. Health regulators like Health Canada will often run Phase 4 trials.

Finding a clinical trial

We have created a webpage with information on clinical trials that are testing innovative treatments. Examples of these treatments are gene and stem cell therapy for inherited retinal diseases like retinitis pigmentosa or age-related macular degeneration.

You can also find more detailed information about these and other clinical trials at If you are interested in joining a clinical trial, speak with your eye doctor.

Unfortunately, not all clinical trials are real studies or safe. There is always risk when joining a clinical trial, but legitimate clinical trials are well regulated to make sure that patients are not put at unnecessary risk.

How do you know if a clinical trial is legitimate?

The website is a major database for clinical trials and has information about trials being conducted around the world. If a clinical trial is trustworthy, it should be listed on the website. If it is not listed this is a major red flag. However, just because a trial is listed here it doesn’t guarantee that it is legitimate. Researchers may post on this website without approval from a regulatory agency like Health Canada or the US Food and Drug Administration (FDA).

These are some other red flags that may indicate that a trial is unregulated or even dangerous:

  • You have to pay to participate in the trial or for any major costs such as medical expenses, travel, or hotel.
  • The trial coordinator or someone on the team tries to convince you that they already know the treatment works.
  • You cannot find out if the trial has been approved by an Institutional Review Board (IRB) or Research Ethics Board (REB). All clinical trials must gain approval from one of these boards before they can recruit patients. Ask the trial coordinator for this information. If they cannot give it to you, this is a red flag.
  • The trial coordinator asks for your social insurance number, or credit card number.

Please do not trust people who are promising unproven miracle treatments that will cost you lots of money. If you find information about a clinical trial or a possible new treatment on or in the news, you should discuss it with your doctor. You can also contact our Health Information Line and we can help you find out more information about the trial.


Below is a video about clinical trials.

If you have eye health-related questions, contact our Health Information Line.

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