Giving patients two or more drugs may provoke various pharmacological effects, either enhance or diminish pharmacological activity of the drug, even more adverse reactions. The rate of adverse reactions(AR) suffered by ordinary patients is in a range of 7,6 to 51,7 according to different literature sources.

The number of potential drug interactions has no limits and the probability of appearance of adverse reaction is directly related to the number of drugs used.

Most of AR does not reveal evident clinical symptoms, and most of them are predictable. Based in these facts, physicians should take them in account before prescribing two or more drugs, avoiding polipharmacy and guaranteeing efficacy and innocuity.