The popular press is full of stories of medical breakthroughs, miracle cures and superfoods. How can we decide which are likely to be true - and which are just there to catch our attention and boost sales? 

Knowing the different stages medical research goes through can help us understand how likely a particular news story is to lead to a medical breakthrough – and how near or far away such a breakthrough is likely to be. The main stages are:

In vitro research (ie in test tubes in the laboratory, over a number of years or possibly even decades).

These in vitro tests often seek to identify the interaction between a small number of cells to demonstrate the effect of a particular chemical/compound on them or the interaction between several cell types. The results obtained from in vitro research may have long term potential but, at this stage, should be interpreted with caution. Human bodies are far more complex than test tubes and other chemicals in the body, such as hormones, will usually be at work and may significantly affect the outcome. So what works in the test tube may or may not work in our bodies.

In vivo research. If the results obtained from these in vitro studies are satisfactory, the next step would usually be to test the effects of the same compound in a species of animal which is not too expensive and easily accessible, such as mice or guinea pigs. This is called in vivo research. At a later (and possibly more controversial) stage this could involve other species which are biologically and physiologically closer to human beings, such as chimpanzees, to establish whether the treatment would be likely to provide reliable results which can be extrapolated and applied in man.   Once again the observations made in these animal models although of potential value, also need to be treated with caution. Laboratory animals in contrast to humans tend to be inbred, which is important because our genetic make-up influences our immune responses. There are also cell types and cell products identified in mice which are not present in man and vice versa. So what works in mice may not work in humans.

Clinical trials in man. If these tests in animal models prove successful, the next steps would involve clinical trials in man which are carried out in 5 phases.

Phase 0: Human microdosing

Phase I: Normally, a small (20-100) group of healthy volunteers will be selected. This phase includes trials designed to assess how safe a drug is and how well it is tolerated by the human body.

Phase II: Once the initial safety of the study drug looks to have been confirmed in Phase I trials, Phase II trials are performed on larger groups (20-300) and are designed to assess how well the drug works, as well as to continue Phase I safety assessments in a larger group of volunteers and patients. When the development process for a new drug fails, this usually occurs during Phase II trials when the drug is discovered not to work as planned, or to have toxic effects .

Phase III studies are randomized controlled trials carried out in a number of centres on large patient groups (300–3,000 or more depending upon the disease/medical condition studied). They aim to be a definitive assessment of how effective the drug is, in comparison with current 'gold standard' treatment. Because of their size and comparatively long duration, Phase III trials are the most expensive, time-consuming and difficult trials to design and run, especially in therapies for chronic medical conditions.

Phase IV trials are also known as Post Marketing Surveillance Trials. They involve the safety surveillance and ongoing technical support of a drug after it receives permission to be sold. Phase IV studies may be required by regulatory authorities or may be undertaken by the sponsoring company for competitive (finding a new market for the drug) or other reasons (for example, the drug may not have been tested for interactions with other drugs, or on certain population groups such as pregnant women, who are unlikely to subject themselves to trials). The safety surveillance is designed to detect any rare or long-term adverse effects over a much larger patient population and longer time period than was possible during the Phase I-III clinical trials. Harmful effects discovered by Phase IV trials may result in a drug being no longer sold, or restricted to certain uses

Epidemiological research. Another type of research involves studying health trends across sample populations and trying to identify which specific factor or factors are making a difference. This is a cornerstone of public health research and involves collecting data about health or disease and seeking to isolate and identify any specific factors which are, for instance, helping transmit or control a disease or affecting health. For example if a large group of people emigrate to another country and adopt the diet and lifestyle of their new country do any health changes become apparent over time?

Epidemiological research findings aren’t as reliable as clinical trials in man. Because of the many different factors potentially involved it can be difficult to be certain, beyond all doubt, that one specific cause (in hygiene, diet, lifestyle, the environment etc) has had one specific positive or adverse effect on health. However, because the research is based on observations of large numbers of people in real life situations (not simply test tube experiments) it is worth serious consideration – and good epidemiological research follows the Bradford-Hill nine point criteria, including the strength, consistency, coherence and plausibility of the findings.

So when you see news of scientific breakthroughs in the media it is worth reading the small print to check how far down the research road the findings are – and therefore how close or far the prospects of a real medical breakthrough.

Published 13/03/2011, Review date May 2015