The presence of very large numbers of non-steroidal anti-inflammatory agents (NSAIAs) on the market is warranted by the wide variation in efficacy from one patient to another and by individual sensitivity in terms of adverse effects. The inhibition of cyclo-oxygenase constituted the only explanation for the mechanism of action of anti-inflammatory agents for many years. The search for products with new pharmacological properties is essentially aimed at improving tolerance. Methods for evaluating the tolerance of NSAIAs, particularly before they are put on the market, must be improved since all NSAIAs pose serious problems due to adverse effects. The risk depends on the nature of the molecule, toxicological data, particularly the effects on the reproductive process, length of treatment, underlying predisposition, and the disease being treated.