Guide to clinical trials
A clear, evidence-informed guide to clinical research and decisions about participation.
What is a clinical trial?
A clinical trial is a planned research study involving people, designed to answer a specific question about preventing, diagnosing, treating or monitoring a health condition. It may investigate a medicine, a combination of treatments, a procedure, a diagnostic test or a non-drug intervention. Unlike routine care, study-specific activities follow a predefined, reviewed protocol. The aim is to generate reliable knowledge—not to guarantee that every participant will improve. A promising treatment may prove ineffective, cause adverse effects or fail during development. Joining a study is voluntary and does not replace usual medical care. The prot
Interventional trials and observational studies
In an interventional study, the protocol assigns an intervention or treatment strategy to assess its effects. It may compare medicines, doses, treatment strategies or other interventions. An observational study collects information from clinical practice or follows people without assigning their treatment under the study protocol. Designs may be prospective, retrospective, cross-sectional or cohort-based. Observational research is valuable for real-world evidence but has limitations when establishing causation. Both types can be found in our Clinical Studies catalogue. “Phase IV” describes a stage of medicine development; “observational” desc
Phases I, II, III and IV
The phase broadly describes a medicine’s stage of clinical development. Some trials combine phases and not every study follows this sequence. Phase I: early studies in humans focusing mainly on safety, tolerability, pharmacokinetics and dosing; volunteers may be healthy or have the condition. Phase II: early evidence of effectiveness, dose selection and continued safety assessment in patients. Phase III: larger comparative studies of efficacy and safety against usual care, active treatment or placebo when justified; often important for regulatory decisions. Phase IV: research after a medicine has been authorised to improve understanding of ef
Why are neurological studies conducted?
Neurology research investigates options for conditions such as multiple sclerosis, epilepsy, migraine, Parkinson’s disease, neuromuscular disorders, stroke and cognitive decline. Outcomes may include seizures, symptoms, function, disease progression, quality of life and treatment safety. Not all research tests new medicines. Some studies examine follow-up strategies, biomarkers, imaging, clinical scales or rehabilitation. Participation contributes to scientific knowledge, although a direct clinical benefit cannot be promised.