Excedrin PM is typically used for pain relief, as a fever reducer and as a sleep aid for individuals unable to sleep due to pain, according to Novartis and Drugs.com. It is an over-the-counter medication that comes in either caplet or gel capsule form, Novartis explains.
Excedrin PM was first introduced by Bristol-Myers Squibb in 1969, states Wikipedia. The medication's active ingredients are acetaminophen and diphenhydramine, according to Drugs.com. Common side effects of the drug include constipation, dizziness, dry mouth, nausea and upset stomach. More severe side effects that may require immediate medical attention include severe allergic reaction with hives or difficulty breathing, irregular heartbeat, dark urine, seizures and hallucinations.