A clinical trial is a research study designed to test the safety and effectiveness of a treatment.

Most often, this is a drug treatment, but any form of treatment can be studied in this way, including surgical treatment, alternative therapies and new techniques such as gene therapy. Clinical trials of drugs usually involve the testing of a newly developed drug, but they can also be done to study new uses for an existing drug, new doses, or new treatment combinations, or to compare existing standard treatments.


Before human trials begin, a new drug usually undergoes extensive testing in animals. These pre-clinical studies are designed to examine the tissue effects of the drug, the way it is processed in the body, and its potential to produce toxicity or birth defects. It must generally also be certified as having been produced according to Good Manufacturing Practice principles and checked for purity and stability.


Phase I trials involve small numbers of individuals.

In these studies, researchers determine the best method of administration (eg, by mouth, IV drip, injection), how often the drug needs to be given, and a safe range of doses. Participants are also monitored very closely to identify any potentially harmful side effects.

Phase II trials involve a larger group of patients to see what treatment effects the drug has, and to further evaluate safety. If the drug appears to be safe, and if its effects look promising, it may progress to the next phase.

Phase III trials are much larger studies, usually involving many hundreds or thousands of patients divided into different treatment groups. The aim is to compare the treatment effectiveness and side effects of the new drug with that of standard treatments (where they exist). If the results of these phased clinical trials show that the drug is safe and effective, it may be registered (licensed for marketing) by the Therapeutic Goods Administration (TGA).

Phase IV studies are conducted after a drug has been released onto the market. They mainly involve comparison with medicines already recognised as having a place in the treatment of the disease or with a range of other therapies.

Post-marketing surveillance
After release of a new drug onto the market, pharmaceutical companies, doctors and the TGA remain on the lookout for rare but important side effects not picked up in earlier clinical trials. Identification of serious side effects can lead to the drug being withdrawn from the market.n


There are many pitfalls in trying to work out whether a new treatment is truly effective. Study results can be influenced by unconscious treatment choices, the expectations of researchers and patients, and a range of other factors unrelated to the treatment. Phase III clinical trials use a number of methods to ensure that the results are reliable. Treatment comparison groups usually involve a test group (given the new treatment) and a control group (given the standard treatment). If there is no standard treatment of proven value, or if it has worrying side effects, a placebo - a look-alike or 'dummy' pill that contains no active drug - may be used in the control group. Allocation to one or other treatment group is generally determined by a computerised lottery method known as randomisation. Ideally, neither researchers nor participants should know which treatment a particular person is having. Studies of this kind are referred to as double blind trials. Safety comes first, though - if a participant develops an unexpected or serious problem while on a trial, the treatment code can be broken and appropriate action taken.


Conducting a clinical trial is a team effort. The team is usually led by a senior clinical researcher - the principal investigator - and may include specialist doctors, general practitioners, nurses, counsellors, pharmacists, laboratory scientists, and many other behind-the-scenes support staff. Because of the large number of patients needed for Phase III clinical trials, these studies are often carried out in many research centres around the world and are known as international multicentre trials. Principal investigators from the major centres often form a steering group to make sure there is proper communication and coordination between participating centres.


All clinical trials must have a sponsor. This can be an individual, a company, an institution, or an organisation that takes responsibility for the initiation, management, and/or financing of a trial. About 80% of clinical trials conducted at SLHD are commercially sponsored and funded, in most cases by a pharmaceutical company. The remainder are initiated by a researcher or group of researchers, and are sponsored by the Local Health District. Funding can come from grant-giving bodies such as the National Health & Medical Research Council or one of the many non-government fund-raising organisations, or researchers and the hospital may absorb the costs of running a trial. It is not considered ethical for clinical trial costs to be charged to patients, health insurance companies, or Medicare. Sometimes, however, patients may be billed for those aspects of their treatment that would otherwise be part of their routine care, such as medical consultations, blood tests, X-rays or scans. Trial participants may be reimbursed for out-of-pocket expenses associated with the trial and, in some studies, you may receive a small amount for the time and inconvenience involved.

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Page Last Updated: 28 November, 2019