Clinical Trial Phases: What’s the Difference?

Clinical trials research potential new treatments, including medication, medical devices, and lifestyle interventions such as diet and exercise. Typically, a potential treatment goes through at least three clinical trial phases before it becomes available to patients.

There are a few differences between each clinical trial phase, including how many volunteers they need and the goal of the trial. If you're considering taking part in a trial, you may want to consider the phase of the clinical trial in making your decision. Depending on your motivations for participating, different phases may be more appealing to you.

Before a potential treatment reaches clinical trials, it's typically tested in animals or hypothesized in another research setting. Researchers only bring treatments to clinical trials if they believe that they will be successful.

After the initial research stage, trials enter Phase 1:

Phase 1: The first phase of a clinical trial tests whether a treatment is safe for people to use – not whether it's effective at treating symptoms. These trials are typically small, with around 20 to 100 volunteers, and may only look for healthy participants who may be compensated for their participation. Some trials may accept those with the condition the drug ultimately aims to target, and while the drug may be effective for these patients, only safety factors will be measured in this phase.

Phase 2: After a treatment has been found safe, in the next clinical trial phase, researchers investigate whether it’s both safe and effective. Phase 2 trials are larger, looking for 100 to a few hundred volunteers. They typically last several months to a few years.

Phase 2 trials may test a potential treatment against either a placebo, the existing standard of care, or another existing drug. Of course, in life-threatening conditions such as cancer, a placebo is rarely used. Most studies are blinded; neither the volunteers nor the researchers know which patients have received the study drug.

Phase 3: These trials typically enroll several hundred to several thousand participants, and continue to test potential treatments for both safety and effectiveness, including watching for treatment side effects.

After a treatment passes this stage, a pharmaceutical company can request FDA approval by sending in a New Drug Application (NDA) to begin marketing the drug to patients.

The FDA then reviews all of the research done on the drug and may require that additional studies be done. If everything looks good, the drug is approved and the drug sponsor can bring it to market.

Phase 4: After a drug or device is already approved, it may enter a Post Marketing Surveillance Trial. Pharmaceutical companies continue to monitor patients taking the treatment to watch for long-term side effects and compare it to existing drugs on the market.

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