When a medicine is marketed for the first time, its effects have been studied on a hundred or at best several thousand patients, but sometimes only a few dozen or so. Studies to determine the optimum dose are carried out on even fewer patients. Efficacy has usually been tested on adults of average age, well selected and without any particular risk. Trials have been carried out according to a very strict protocol, in conditions very different to those encountered in the daily life of patients. Information on side effects is patchy, owing to the small number of those treated and the short time of use. Interactions with other medicines have only been studied in a few dozen subjects.

Following marketing approval, tens or hundreds of thousands of patients will use the medicine, maybe more. The patients are going to take the medicine in different conditions than those used during the development: along with other medicines, foods, alcohol, and perhaps with more or less regularity. The elderly and people at risk due to associated illnesses may show unexpected side effects. Some patients may take higher doses; drug abuse can occur. Others may take a dose too small or irregularly because they do not feel the intended effect or because the medicine is difficult to take. For others, smaller doses may prove sufficient. Side effects whether mild or serious may appear.

In the mean time, other medicines could prove to be more effective, or equally effective but safer, more convenient, or starting to act more quickly. Information on the epidemiology of the targeted illness may challenge the use of the medicine in some situations. Publication of reports can prompt a re-appraisal of the benefit and risk that can tilt the balance in favour of or away from use of the medicine.

For example, since the 1960's, spironolactone had been mainly used as a diuretic for short-term symptomatic treatment. In 1999, a trial showed a substantial reduction in mortality of people with cardiac failure, which led to extend the use of spironolactone in favour of selected patients.
Conversely, it turned out that cisapride, a symptomatic treatment for nausea and gastro-oesophageal reflux, could cause fatal cardiac arrhythmia while omeprazole was more effective.

It is neither scientifically nor ethically acceptable to allow emerging information about medicines to fall by the wayside. To let a medicine on the market without regularly re-assessing the balance between its benefits and side effects as compared with other available treatments, can be detrimental to some patients.

Medicines in Europe Forum demands a regular, thorough and well-conducted re-evaluation of medicines, as well as corresponding updates on information for health professionals and patients. It would not be responsible and ethical to grant marketing authorisations indefinitely.