FreeBioListMost rows in our tracker are clinical readouts, labelled by phase: Phase 1, 2 or 3, and in-between steps like 1b or 2/3. The phase tells you what question the trial was designed to answer, and that's the key to reading its result. A "positive" Phase 1 and a "positive" Phase 3 are different kinds of news.
Before Phase 1: the IND
A company can't test an unapproved drug in people in the US until it has filed an Investigational New Drug application (IND) with the FDA, under 21 CFR Part 312. The IND contains the laboratory and animal data, how the drug is made, and the plan for the first human study. If the FDA doesn't place it on hold within 30 days, the trial can begin. A "clinical hold" stops trials until the FDA's concerns are resolved, and companies generally disclose one when it happens.
Phase 1: is it safe, and what dose?
Phase 1 trials are the first time a drug is given to people. The FDA's overview of clinical research puts them at roughly 20 to 100 participants. The main questions are safety, how the body absorbs and clears the drug (pharmacokinetics), and which dose range to carry forward.
Many Phase 1 trials enrol healthy volunteers. In cancer and some rare diseases they enrol patients instead, because the drug's risks only make sense for people who might benefit. Doses usually rise step by step through small groups ("dose escalation") until the investigators find the highest dose people tolerate or the dose that does what they need.
What a Phase 1 readout can tell you: whether the drug was tolerated, how it behaves in the body, and sometimes early signs of biological activity (a biomarker moving, for instance). What it can't: whether the drug works, because the trials are small, short and often have no control group.
Seaport Therapeutics reported a Phase 1 driving-simulation study of GlyphAllo in healthy volunteers, designed to check that evening doses didn't impair next-morning driving (press release, 9 September 2026). It's a good example of a Phase 1 trial asking a narrow safety question rather than an efficacy one. See the Seaport page.
Phase 2: does it seem to work?
Phase 2 trials enrol people who have the condition, up to several hundred of them, and are the first real test of whether the drug does anything useful. They're often randomised and compared with placebo, and they're used to choose the dose and the endpoints for Phase 3.
Two sub-labels are common:
- Phase 2a: smaller, earlier "proof of concept" studies, often looking for a signal on a biomarker or a short-term clinical measure.
- Phase 2b: larger, more rigorous dose-ranging studies, sometimes big enough to look like a small Phase 3.
What a Phase 2 readout can tell you: whether there's a credible efficacy signal and at which dose. What it can't: whether that signal will hold up in the larger, more varied population of a Phase 3. Phase 2 success rates are notably higher than Phase 3 ones for this reason.
Roivant's Phase 2 PHocus study of mosliciguat in pulmonary hypertension with interstitial lung disease met its primary endpoint, a placebo-adjusted reduction in pulmonary vascular resistance, and the company said it was moving to a global Phase 3 (8-K exhibit, 8 September 2026). That's the normal Phase 2 job: produce enough evidence to justify a larger trial. See the Roivant page.
Phase 3: the confirmatory trials
Phase 3 trials are large (the FDA's overview gives roughly 300 to 3,000 participants), usually randomised and blinded, and designed to confirm efficacy and build the safety database needed for approval. They're often called "pivotal" or "registrational" because they're the studies the application rests on.
A Phase 3 readout is the most consequential clinical event for most companies, and it has its own guide: how to read a Phase 3 topline readout.
Combined labels: 1/2, 1b/2 and 2/3
Companies increasingly run "seamless" trials that move from one phase to the next under a single protocol, to save time. A Phase 1/2 trial starts with dose-finding and expands into a larger group at the chosen dose. A Phase 2/3 trial is designed so that the early part can inform or roll into the confirmatory part. Rare-disease and gene-therapy programmes use these designs a lot, because there may not be enough patients to run separate trials.
The label tells you the trial's ambition, not which stage a particular readout is from. An "interim" readout of a Phase 2/3 trial may be the Phase 2 portion, so check what the release says the data actually are.
In our tracker, the Phase column sorts these in their natural place: a Phase 1/2 readout sorts between Phase 1 and Phase 2, and a Phase 2/3 between Phase 2b and Phase 3.
Phase 4: after approval
Phase 4 studies happen after a drug is approved. Some are required by the FDA as a condition of approval: to confirm benefit after an accelerated approval, to study long-term safety, or to test the drug in children. Others are run by the company to support new uses or marketing. They rarely move the dial on their own, but a failed confirmatory study after an accelerated approval can lead to the indication being withdrawn.
From the last trial to the FDA
After the pivotal data, a company typically holds a pre-NDA or pre-BLA meeting with the FDA, assembles the application, and submits it. Our tracker records the submission as a "Regulatory submission" row when the company guides to one. Once the FDA accepts it, a PDUFA date follows. NDA versus BLA explains which application a product needs.
Why phase matters when you read a date
- Earlier phases fail more often, and their "positive" results mean less on their own.
- Readout timing is less certain earlier on, because small trials are more exposed to recruitment delays. That's one reason most readout rows show a window rather than a date; see why catalyst windows are vague.
- A late-stage readout and a regulatory decision for the same drug can sit months apart. A company page on this site lists them together so you can see the sequence.