The effectiveness of restricting access to certain means of committing suicide has been demonstrated, at least as regards toxic domestic gas, firearms, drugs and bridges. At the individual level, studies tend to indicate that many persons have a preference for a given means, which would limit the possibility of substitution or displacement towards another method. Similarly, the fact that suicidal crisis are very often short-lived (and, what is more, influenced by ambivalence or impulsiveness) suggests that an individual with restricted access to a given means would not put off his plans to later or turn to alternative methods. This has been more difficult to demonstrate scientifically in population studies. Nevertheless, it appears that, should such a shift occur towards other means, it would be put into effect only in part and over a longer term.