• Excedrin PM contains 500 mg of acetaminophen to alleviate minor pain and 38 mg of diphenhydramine citrate, an antihistamine, as a sleep-aid. The combination of medications can be helpful in treating fever, pain, sneezing, runny nose and cold/flu symptoms. Like all medications, there are risks associated with Excedrin PM, including liver damage, overdose, drowsiness-related accidents, medication interactions, worsening of certain conditions and potential effects on unborn babies and infants.
  
  

Liver Damage

• Acetaminophen may cause serious damage to the liver and should not be used in patients with liver disease without a doctor's guidance. To avoid liver damage, do not drink more than two alcoholic beverages per day while using Excedrin PM. Consumers should not take more than the recommended dosage. Additionally, Excedrin PM should not be taken with any other medication that contains acetaminophen.
  
  

Overdose

• To avoid accidental overdose, Excedrin PM should not be taken with any other medications that contain acetaminophen or diphenhydramine. According to Drugs.com, overdose of acetaminophen is among the most common poisonings around the globe. Symptoms of acetaminophen overdose include diarrhea, nausea, stomach pain, diminished appetite, vomiting, moodiness, increased perspiration, convulsions and coma. An overdose of diphenhydramine may cause symptoms such as dry mouth, drowsiness, diarrhea, abdominal pain, agitation, blurry vision, flushed skin, nausea, confusion, increased heart rate, trouble moving, trouble speaking, difficulty urinating, low-grade fever, delirium, convulsions and coma.
  
  

Drowsiness-Related Accidents

• Consumers who take tranquilizers or sedatives should check with a pharmacist or doctor prior to taking Excedrin PM. This medication is designed as a pain reliever and a sleep aid. Diphenhydramine may cause sleepiness. Drinking alcoholic beverages while taking Excedrin PM may increase medication-related drowsiness. To avoid potentially serious accidents, consumers should use caution prior to driving a car or operating any heavy machinery until the medication's effects are well known.
  
  

Medication Interactions

• Certain medications may interact with Excedrin PM, including diuretics, antidepressants, urinary medications, isoniazid, zidovudine, aspirin, medication for irritable bowel syndrome, gout medications or seizure medications. Do not use Excedrin PM prior to talking to a doctor or pharmacist about all prescription medications, over-the-counter medications and herbal supplements that may interact with it.
  
  

Worsening Other Medical Conditions

• According to Excedrin PM's product information, taking Excedrin PM may worsen certain conditions, including liver disease, breathing problems, urinary disorders, enlarged prostate, glaucoma or kidney disease. Patients with these conditions should consult a doctor prior to using Excedrin PM.
  
  

Potential Harm To Babies

• According to Drugs.com, the effect of acetaminophen and diphenhydramine on an unborn baby is unknown. Additionally, the medication may pass through breast milk and affect nursing babies. Pregnant or nursing mothers should consult a doctor prior to using Excedrin PM.