by Nicole Evans M.D.

Created on: March 28, 2010

Tylenol PM is a popular over-the-counter medication.  The labeled indicated use for Tylenol PM is for the relief of insomnia that is accompanied by minor pain.

The two active ingredients in Tylenol PM are Acetaminophen (Tylenol) and Diphenhydramine (Benadryl).  The acetaminophen provides pain relief while the diphenhydramine induces sleepiness.  The side effects of Tylenol PM can result from either or both of these medicinally active agents.

The side effects of Tylenol PM that result from the acetaminophen component can affect the skin, liver, kidneys, blood and even the endocrine system.  The frequency of these Tylenol side effects is not defined but include: rash, anemia, low neutrophil count, low leukocyte count and pancytopenia (low white blood cells, red blood cells and platelets).

Tylenol PM use can also result in increased bilirubin and/or alkaline phosphatase levels, high ammonia levels, kidney damage with chronic high doses of Tylenol and increased blood sugar levels.

Perhaps the most important potential adverse effect of Tylenol PM is liver toxicity.  An acute overdose of Tylenol PM can result in liver failure and death.  The dose of acetaminophen should never be more than 4 grams a day.

In addition, chronic daily dosing in adults has resulted in liver damage in some people.  It is known that consuming 3 or more alcoholic drinks a day may increase the risk of liver damage from Tylenol.

Additionally, individuals with the inherited condition known as G6PD deficiency should use caution when taking medications that contain acetaminophen.

The other active ingredient in Tylenol PM, diphenhydramine, is commonly known as Benadryl.  Benadryl is a first-generation antihistamine that is quite sedating, unlike the later generation antihistamines such as Zyrtec and Claritin. 

Common side effects of Benadryl include sedation, sleepiness, dizziness, difficulty performing coordinated movements, epigastric distress (stomach ache), and thickening of mucus secretions from the respiratory tract.

Importantly, when giving Benadryl to children by mouth and using a concomitant topical preparation that contains Benadryl there is a risk of diphenhydramine toxicity.  The symptoms of Benadryl toxicity include: dilated pupils, flushed face, hallucinations, ataxic gait, and urinary retention.

In children, there is also the risk of diminished mental alertness, as well as risk of a paradoxical reaction that may cause excitation in young pediatric patients.

There are certain medical conditions that require a patient consult their physician before self-treating with over-the-counter Benadryl preparations.  These conditions include glaucoma, emphysema, chronic bronchitis, or difficulty urinating due to prostatic hypertrophy.

Tylenol PM is a commonly used over-the-counter medication that is associated with numerous side effects.  For safety, individuals should always discuss the use of Tylenol PM with their healthcare provider.

Source: Lexi-Comp Online. Accessed Mar 27, 2010.

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