The interest in generic medicines comes from the health systems' need to reduce the health bill without decreasing health objectives. Their expansion and use requires their acceptance by the general public and by professionals. It also requires some doubts about their genuine equivalence to the original drugs to be cleared up. Since their introduction on the drug market, there has been some debate about whether or not they are correctly researched and of high enough quality. It is not infrequent to find mistaken concepts among professionals about generic medicines, particularly the alleged claim that they may contain up to 20% less concentrate of the main ingredient. These mistaken beliefs suggest there is a disadvantage in the efficacy and tolerability of generic medicines compared to their brand counterparts, decreasing credibility in them. Therefore, in a survey carried out in 2008, pharmacists stated that generic drugs and brand-name drugs were different with regard to efficacy (26%), equivalence (28%) and, above all, the quality of the excipient (46%), increasing the perception that generic drugs are different depending on which laboratory manufactures them (52.8%). In this article, in order to increase knowledge about generic drugs, to solve doubts and to provide information which is objective, clear and rigorous, possible prejudices about generic drugs are reviewed and evidence, such as the bioequivalence requirements of generic products, is given about them, analysing whether their therapeutic and exchange equivalence is being suitably corroborated.