A clinical trial is a research study into a new therapies, vaccines or new ways of using known treatments to determine the safety and efficacy of a drug before it reaches the public. Clinical trials are also referred to as medical research or research studies.

Trials are conducted in four phases with an increasing number of patients enrolled at each phase:
Phase I – involves a small number of participants and tests the actions of the drug in humans
Phase II – evaluates the drug for a particular indicated use
Phase III – gathers additional evidence on a drug once preliminary effectiveness has been proved
Phase IV – ongoing research after the drug has gone to market

See also:
Phase I trials
Phase II trials
Phase III trials
Phase IV trials
Clinical trial enrolment
Pre-clinical trials
International Clinical Trial Registry Platform (ICTRP)
Placebo
Placebo-controlled studyBaseline
Bias
Blind
Brief Summary
Baseline
Blind (clinical treatment)
Clinical Trial Enrolment
Clinical
Cohort
Control Group
Controlled Trial
Diagnostic Trials
Dichotomous Question
Dose-ranging Trial
Double blind Trial
Drop Out
Drug-drug interaction
Effectiveness
Efficacy
Eligibility Criteria
Endpoint
Experimental Drug
Informed Consent
Methodology
Open label Trial
Pre-clinical Trials
Prevention Trials
Quality of Life Trials
Randomisation
Randomised Trial
Risk-benefit analysis
Screening Trials
Single-blind Trial
Trial endpoint
Treatment Trials
Adverse Event
Adverse Reaction