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Clinical trials with medicines for human use

Last update: September 08, 2025

A clinical trial with medicines for human use is an investigation in relation to humans, in order to study drug safety and efficacy. The purpose of these studies is to get relevant data that prove a positive benefit/risk profile for a certain therapy so that marketing authorization can be requested.

There are several stages during clinical investigation where study population progressively increase:

  • Phase I: a few participants (tens) that can be healthy volunteers, to confirm that drug administration is safe.
  • Phase II: efficacy analysis in a 200-300 people study population, while safety for phase one doses is still monitored.
  • Phase III: drug efficacy confirmation among thousands of participants so that data can be obtained to get a marketing authorization.
  • Phase IV: long-term studies with authorized medicines to study rare adverse drug reactions or additional benefits.

The Spanish Agency for Medicines and Medical Devices (AEMPS) is the national competent authority to grant an authorisation for a clinical trial with medicines for human use. Nevertheless, assessment of both scientific and ethic aspects is done by AEMPS and Ethics Committees for Investigation with medicinal products (CEIm) on a coordinated procedure.

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