CT (Clinical Trial)
What is it?
A clinical trial is a controlled study in human participants, run in phases (I through IV), used to establish whether a medicine is safe and effective before and after approval. Phases I to III happen pre-authorization, building the safety and efficacy case a marketing authorization is granted on. Phase IV happens after approval, and overlaps directly with pharmacovigilance: it's where post-authorization safety studies and real-world follow-up live.
For safety teams, the trial context matters because reporting rules differ from routine post-marketing case processing. A suspected unexpected serious adverse reaction (SUSAR) occurring in an ongoing trial has its own expedited reporting pathway to trial authorities and ethics committees, separate from standard ICSR submission for an already-approved product.
The four phases
Safety reporting rules shift as a trial moves through its phases. Click one to see what changes.
Click a phase to see its detailPhase I: the first time the medicine is tested in people, usually a small group of healthy volunteers, to check safety and find a workable dose.
Phase II: tested in patients who actually have the condition, to get a first read on whether it works and what side effects show up.
Phase III: a large, often multi-country trial confirming the effect holds up at scale, the evidence a marketing authorization actually gets granted on.
Phase IV: happens after approval, once the medicine is already on the market. This is where clinical trial work and pharmacovigilance directly overlap.
CTIS replaced EudraCT. Since 2023, the EU's Clinical Trials Information System is the single portal for authorizing and overseeing trials across member states, including SUSAR-related transparency, replacing the older EudraCT database.
Common Misconceptions
"Once Phase III succeeds and the medicine gets approved, its safety profile is basically settled."
Even a large Phase III trial only enrolls a few thousand carefully selected patients over a limited stretch of time. Rare reactions, drug interactions, and long-term effects often only surface once far larger, far messier real-world populations start taking the medicine, which is exactly why Phase IV and ongoing pharmacovigilance exist.
