There is no firm definition of polypharmacy, but the American Family Physician website mentions the regular use of five drugs as a benchmark. These can be prescription or over-the-counter drugs. People see multiple doctors so end up with many prescriptions, sometimes working at cross purposes to each other. Which is why occasional assessment of a patient's overall drug regimen is recommended. The American Geriatrics Society developed the the Beers Criteria as a tool for healthcare providers to check for possible dangerous combinations of medicines.
There are actually two phenomena that people use the term polypharmacy to describe:
Polypharmacy happens to people of all ages, but it is particularly prevalent among the elderly. More than 90 percent of old people use more than one medicine - on an average people use four medications.
Related to polypharmacy is multimorbidity, which means a person has more than one chronic health condition. More diseases usually means more medicines. In addition to the risk of drug-drug interactions, polypharmacy in a person with multiple conditions increases the chances of a drug making another disease (not the one it is intended to treat) worse. Pharmacodynamics - how a medicine affects a person given different biochemistries and genetic profiles - is difficult enough for experts to work out when it is just one medicine and one condition. Factoring in different medicines and different conditions makes it all the more complex.
The bodies of older people are less efficient at processing drugs through the body. Renal and hepatic function can be reduced. So any medicine is more fraught with risk in the elderly than in younger people.
Compliance is defined as the degree to which a patient correctly follows medical advice. Although the terms are related, compliance suggests that the patient is passively following the physician’s orders, while adherence acknowledges that the patient is part of the decision-making process, making this the preferred term. Another frequently encountered word is “persistence,” defined as the duration of time over which a patient continues to fill the prescription.