Tylenol PM is an over-the-counter medication composed of acetaminophen and diphenhydramine. This drug combination can be used to treat such symptoms as a runny nose, watery eyes, sneezing, pain or fever associated with a cold, the flu or allergies. Tylenol PM is also used to treat sleeplessness and nighttime pain.
Acetaminophen
The primary ingredient in Tylenol PM is acetaminophen, a pain reliever and fever reducer. Acetaminophen reduces fever and mild to moderate pain such as headache or muscle ache by inhibiting the action of prostaglandin, a chemical signal that results in fever and pain. According to Tylenol.com, every dose of Tylenol PM contains 500 mg of acetaminophen. Acetaminophen is not usually associated with side effects; however, prolonged use of maximum doses of Tylenol PM, especially 4 g per day, can result in severe liver damage.
Diphenhydramine
According to Tylenol.com, each dose of Tylenol PM contains 25 mg of diphenhydramine. Diphenhydramine is an antihistamine that works by blocking the release of histamine, an inflammatory chemical released by the immune system during an infection or allergic reaction, notes Drugs.com. By blocking the effects of histamine, diphenhydramine prevents sneezing, nasal drainage, watery eyes and other allergic symptoms. Diphenhydramine also blocks the action of histamine in the brain, thereby preventing sleeplessness.
Inactive Ingredients
Tylenol PM also has a number of inactive ingredients known as excipients. Ingredients such as magnesium stearate, polyethylene glycol, red iron oxide, hydromellose, titatinium dioxide, microcrystalline cellulose, propylene glycol, sodium citrate sodium starch glycolate, sodium lauryl sulfate and sodium propionate are added to Tylenol PM, notes Tylenol.com, to act as fillers and binders, helping to keep the active ingredients intact and assisting in the absorption of the medicine in the gastrointestinal tract.
