Adverse drug effects are encouraged by multiple drug use; interactions between medications may alter their intended therapeutic effect. Multiple prescriptions are common, particularly within the present fragmented health system in which a person’s care may be divided among various specialists. In addition, people are often misinformed concerning the identity, purpose, side effects and dosage instructions for their medications. Improper storage may alter the properties of drugs or even make them strongly toxic. For example, outdated tetracycline can cause kidney damage; nitroglycerin can deteriorate quickly if exposed to light or moisture.