Clinical trials are studies designed to test treatments and diagnostic tools on volunteers prior to use on patients.

For medical practitioners to ethically prescribe a drug, device, therapy, or test, they have to be confident it not only works, but it produces few significant side-effects and doesn't interfere with other tests and treatments.

Governments around the globe have administrative bodies that require a product's clinical testing before it can be legally used in healthcare. This doesn't just apply to new inventions - it can include traditional practices that have been around for generations. On average, around 14 percent of medications being tested make it all the way through for approval by the US Food and Drug Administration.

There are typically several levels or 'phases' of clinical trial scientists must move through before the product can be considered by a government authority for public use.

Preclinical research

To show a new medication or procedure will be safe on human volunteers, researchers will do their homework.

This often means running small, relatively inexpensive tests on animals or tissue samples to rule out dangerous complications. Not only will it help reveal any potentially life-threatening consequences, it helps researchers better calculate things like appropriate dosages and testing conditions.

Phase 1 clinical trial

The first phase of clinical testing assesses safety. It can take just a few weeks to months to complete, and involves at least 20 healthy volunteers who are paid for their time and risk.

The goal of these studies is a measure of physiological effects on people who don't have any significant health conditions. The measures include details on how a drug is metabolised, absorbed, and excreted.

Phase 2 clinical trial

The second phase of clinical testing assesses efficacy. It generally involves hundreds of patients who are likely to benefit from the drug, treatment or test, and can take months or even years to process completely.

To rule out patient or researcher expectations influencing how outcomes are interpreted, many phase 2 trials are based on experimental designs that help reduce bias. This can include randomly assigning test subjects to one of two groups - one that includes the method or material being tested, and a second group using tests that superficially resemble the first group.

This alternative 'fake' group is often referred to as a sham or placebo. Comparisons between the groups can help determine whether apparent benefits could potentially be the result of patient expectations.

Phase 3 clinical trial

The third phase of clinical testing compares risks and benefits. It's designed to expand on the results of phase 2 trials, providing necessary details on less common side effects, potential conflicts, or long-term complications.

They typically involve hundreds to thousands of patients and can last years, providing government administrators and medical practitioners with an appropriate level of information to help them determine whether the medical tool or drug being tested is worth its costs and risks.

Post-clinical research

Sometimes there are surveillance or 'phase 4' trials which continue to follow up patients in the field over a long period of time, to collect information on cost effectiveness or long-term risks and benefits.

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