Most people don’t realize that every medicine, vaccine, or medical device they use—from insulin to inhalers—went through a long, careful process before it was approved. Clinical trials are how we make sure these treatments are safe and actually work. But before anything is tested in people, there’s a lot that happens behind the scenes.
Before a treatment ever reaches a person, scientists spend years studying it in the lab. This is called preclinical research.
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Discovery: Researchers study how diseases work and look for new ways to treat or prevent them—like blocking a protein that causes symptoms or creating a new type of insulin.
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Lab Testing: They test the new treatment on cells in test tubes to see if it has the effect they expect.
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Animal Studies: If it looks promising, the treatment is tested in animals to check for safety and side effects.
Only when these early steps show that a treatment might work and appears safe, can the company or researchers apply to begin human trials. The FDA must approve this application before any testing in people begins.
Clinical Trial Phases (Human Testing)
Once the treatment is approved for human trials, it goes through four phases of testing. Each phase builds on what was learned in the last and involves more people.
Goal: Test safety, not effectiveness
People involved: 20–100 healthy volunteers or patients
Timeframe: Several months
In Phase 1, the treatment is given to a small group for the first time.
Researchers want to know:
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Is it safe?
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What are the side effects?
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What’s the right dose?
This is where doctors carefully monitor every response to find out how the body reacts.
Think of this phase as “testing the waters.”
Goal: Start testing if it works, while still watching safety
People involved: 100–300 patients with the condition
Timeframe: Several months to 2 years
Now that it seems safe, the treatment is given to a larger group of people who actually have the condition. This is where researchers begin looking for early signs that the treatment works.
They may also compare it to:
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A placebo (a sugar pill or inactive treatment)—but not always
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The current standard treatment
Many people worry they’ll be “taken off” their current medicine. That’s rarely true. Most trials today add the new treatment alongside usual care or only include people who are stable enough to try something new safely.
Phase 2 asks: “Is this starting to help real people?”
Goal: Confirm effectiveness and monitor side effects in a large population
People involved: 300–3,000 (sometimes tens of thousands)
Timeframe: 1–4 years
This is the final big test before the treatment can be approved for public use.
Doctors compare the new treatment to what’s already on the market, checking:
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How well it works
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What side effects appear over time
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How it performs across different age groups, races, and health conditions
This phase often looks like real-world medical care, but with extra attention and data tracking.
If the results are strong, the company can apply to the FDA for approval.
FDA Review and Approval
Once all trial data is collected, it’s sent to the FDA (Food and Drug Administration) for review. They check:
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Is it safe?
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Does it work?
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Do the benefits outweigh the risks?
If yes, the treatment is approved and made available to the public.
Goal: Track safety and effectiveness over time
People involved: The general public using the product
Timeframe: Ongoing
Even after approval, the story isn’t over. Doctors and researchers keep tracking how the treatment works in the real world. They want to know:
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Are there rare side effects that didn’t show up earlier?
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Does it work long-term?
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Is it safe for pregnant people or children?
Sometimes treatments are updated or recalled based on this phase.
Even medications as common and well known as aspirin continue to be tested in phase 4 trials.