Clinical trials and FDA approval, step by step
How a molecule goes from a lab idea to an approved medicine, and why most never make it.
VALREXA Biosciences · 8 min read · November 2026
- A drug passes through lab and animal studies, then three phases of human trials, before FDA review.
- Roughly one in ten drugs that enter human trials is eventually approved.
- Expedited pathways speed review, but accelerated approval still requires a confirmatory trial.
Before people: preclinical research
New candidates are first tested in cells (in vitro) and in animals (in vivo) to learn how they work, how the body handles them, and whether they are toxic. If results look promising, the sponsor files an Investigational New Drug (IND) application with the FDA, describing the data and the plan for human studies.
The three phases of human trials
| Phase | Typical size | Main question |
|---|---|---|
| Phase 1 | 20–100 people, often healthy volunteers | Is it safe? How does the body absorb and clear it? |
| Phase 2 | Up to several hundred patients | Does it work, and what are the side effects? |
| Phase 3 | About 300–3,000 or more patients | Does it work better than a placebo or current treatment in a large, diverse group? |
| Phase 4 | Thousands, after approval | What happens in real-world use over the long term? |
FDA review
After Phase 3, the sponsor submits a New Drug Application (NDA), or a Biologics License Application (BLA) for biologics. FDA reviewers examine the data, the manufacturing process and the proposed label. The FDA’s goal is to act within about 10 months for a standard review and about 6 months for a priority review, counted from when the application is accepted. Outside experts on an advisory committee may vote on a question, but their vote is a recommendation, not a decision.
Expedited pathways
| Pathway | What it does |
|---|---|
| Fast Track | More frequent meetings with the FDA and rolling submission, for serious conditions with unmet need |
| Breakthrough Therapy | Intensive FDA guidance when early evidence shows substantial improvement |
| Priority Review | A shorter review goal (about 6 months) |
| Accelerated Approval | Approval based on a surrogate endpoint likely to predict benefit, such as a lab value or muscle strength, with a required confirmatory trial |
An example: in September 2025 the FDA granted accelerated approval to elamipretide (Forzinity) for Barth syndrome, based on improved knee-muscle strength, and required a randomized trial to confirm real-world benefit.
Why most drugs fail
Analyses of industry data estimate that only about one in ten drugs entering Phase 1 is eventually approved. The most common reasons are that the drug does not work well enough in people, or that safety problems appear. This is why early-stage results, however exciting, are not proof. See The evidence pyramid.
Finding trials yourself
Since 2007, U.S. law has required most trials of FDA-regulated products to be registered on ClinicalTrials.gov, and many must post results. Each trial has an NCT number. Every VALREXA profile links to the relevant registry search.
Further reading
- FDA: The drug development process
- FDA: Fast Track, Breakthrough Therapy, Accelerated Approval, Priority Review
- ClinicalTrials.gov: Learn about clinical studies
These are authoritative background resources rather than citations to a specific experimental finding. This guide is educational, not medical advice, and does not endorse the use of experimental compounds.