In medicine, adverse effects are side effects of medication that are unintended and often of a harmful nature.
These can be caused by inappropriate use or improper dosage of a medication or a patient's previously unknown sensitivity to the medication. The adverse effects of medications are a frequent cause of a patient's non-compliance with prescribed treatment. Many of us have had the occasional experience of a medication that makes you wonder what is worse, the ailment or the medication? Unfortunately, patient non-compliance with treatment can, in some cases, be fatal.