Before drugs are marketed, they are extensively tested in animals and in clinical trials in humans. These tests tell much about the drug's efficacy but for several reasons relatively little about safety (box).
Good economical reasons preclude an endless quest for research before drugs are registered. Such research would make the development of drugs expensive, a price that ultimately is paid by the consumer.1
More effort therefore should be put into researching the safety of drugs after marketing, especially in the evidence-free zone when drugs are first launched.2
Protecting society against the adverse effects of drugs requires early detection, valid verification, and quantification, which include assessing the frequency and severity of adverse events, dose relations, the time course, and susceptibility factors.3
In daily practice many signals of a potential adverse event are not followed by a systematic process of verification and quantification. One reason for this may be the transitional period between the signal of a problem and its confirmation. At this point every sensible professional response is open to discussion. If the problem is highlighted by a single case report, attention may fade; even if similar signals are produced by other case reports, the likelihood of a causal relation is often just debated unless more evidence emerges. Subsequent well designed epidemiological studies may provide additional verification. They also fulfil the need for quantification of the adverse effect. Whether such studies are performed usually depends on the initiatives of scientific groups with an interest in the topic. Another reason why safety issues may not be pursued systematically is related to who has the responsibility. Formally, liability rests with the pharmaceutical company, which acts as marketing authorisation holder, but as it does not have an economic interest in detecting safety issues it may lack incentive to investigate problems. Additionally, many problems related to a drug are caused by class effects, such as extrapyramidal effects due to neuroleptics. Then it is not always possible to blame a particular product or company. Drug authorities should take responsibility to safeguard public health in such a situation.