A clinical trials registry (CTR) is an official platform for registering clinical trials so that information about the trial is publicly accessible by researchers, patients and the general public.

It is often a legal requirement for clinical trials conducted in many countries to be registered. Some countries require clinical trials being conducted in that country to be registered; others do not require it, but will often strongly encourage it.
ClinicalTrials.gov run by the United States National Library of Medicine (NLM) was the first online registry for clinical trials and is the largest and most widely used today.

Others include the WHO International Clinical Trials Registry Platform and the Pan African Clinical Trials registry.
Another strong incentive to register a trial is that most funders insist on registration of any trial that they are funding, and also that most journals will not publish a trial unless it was registered BEFORE the first patient is recruited (ref ICMJE requirements, July 2008).

Why Register a Trial?
There are both ethical and scientific reasons for registering trials. The clinical trial registry reduces selective publication of clinical trial results, since they increase the visibility of all research conducted.
One of the key advantages of the registry is that researchers can learn from other trials. For example, in a case where a novel therapeutic strategy is associated with adverse events, information about these outcomes would be in the database, even if the product were subsequently abandoned by the manufacturer. That way, if another researcher pursued the same intervention, the trial designers would be aware of the potential dangers and could develop means for monitoring and mitigating against potential toxic effects.
Nowadays, most countries have a clinical trial registry.

In 2011, the European Medicines Agency launched its online register which gives the public access to information on interventional clinical trials for medicines authorised in the 27 EU Member States, including, Iceland, Liechtenstein and Norway. The database also allows the public to search for information on clinical trials authorised to be carried out outside the EU if these trials are part of a Paediatric Investigation Plan (PIP).
The information contained in the EU Clinical Trials Register is obtained from the EU Clinical Trials Database, EudraCT. This is information is provided by the sponsor when they apply to their national regulatory authority to conduct clinical trials.

Similar clinical trial databases now exits all over the world: The WHO’s trial registry, is globally applicable. African trials can be registered in the Pan African Clinical Trial Registry (PACTR), Australia and New Zealand share the same clinical trial registry, known as the Australia and New Zealand Clinical Trial Registry (ANZCTR). Clinical Trial registry exists in other countries such as India, China, Brazil, Sri Lanka, Japan etc.

Why is Trial Registration Important?
The registration of all interventional trials is considered to be a scientific, ethical and moral responsibility because:

- The clinical trial registry provides a reliable source of information on the efficacy and safety of prevention and treatment measures
- Regulators, researchers and patients can make an informed decision if publication bias and selective reporting is eliminated.
- Improving awareness of similar or identical trials will make it possible for researchers and funding agencies to avoid unnecessary duplication.
- Describing clinical trials in progress can make it easier to identify gaps in clinical trials research, thereby ensuring effective use of limited research funding.
- The status of clinical trials (such as ongoing, recruiting or closed) could attract potential patients looking for novel treatment and therefore aid recruitment.
- The register will enable researchers and health care practitioners to identify trials in which they may have an interest and could facilitate more effective collaboration among researchers.
- Registries checking data as part of the registration process may lead to improvements in the quality of clinical trials by making it possible to identify potential problems early in the research process

What is the definition of a trial?
The journals use the WHO definition of a clinical trial, which is given as follows:
‘Any research study that prospectively assigns human participants or groups of humans to one or more health-related intervention to evaluate effects on health outcomes (Now includes phase I and also a broader definition of interventions)’

In practice this means that any research into human subjects, where there is an intervention is a trial: the intervention could be anything: a drug, a vaccine, a type of surgery, counselling, or a text message reminding patients to take their medication. The intervention could be distant from the actual patients. For example, you could randomise groups of community health workers in Africa into two groups, and then train one with a new method to teach mothers how to give antimalarial treatments, and not provide the specialised training to the other groups of nurses: this is still a trial because patients are seeing nurses who are assigned to one group or another. This would need to be registered.

Conclusion
Previously, researchers reported favourable or successful trials, while negative results were often unpublished and unfavourable results could therefore be easily hidden. Now, trial registries at least provide a searchable database of all trials so the existence of all studies is known, and if they are not published then the investigators can be asked for the data. The aim is for this to be beneficial to researchers, patients and funding agencies as a result of the transparency registries bring.

References
- WHO International Clinical Trials Registry Platform - http://www.who.int/ictrp/en/
- Prayle A.P “Compliance with mandatory reporting of clinical trial results on ClinicalTrials.gov: cross sectional study” British Medical Journal 2012; 344:d7373
- Jeffrey M. Drazen “Transparency for Clinical Trials — The TEST Act” New England Journal of Medicine 2012 364: 863 - 864.
- ICMJE Update on Trial Registration: Clinical Trial Registration: Looking Bavck and Moving Ahead (June 2007) http://www.nejm.org/doi/full/10.1056/NEJMe078110#t=article