Acetaminophen

• Acetaminophen, commonly sold over the counter as Tylenol and a part of some prescription pain relievers like Vicodin and Percocet, carries the risk of serious and possibly fatal liver injury. This risk is low and can be reduced even further by taking acetaminophen as directed and avoiding alcohol with the medication, according to the Food and Drug Administration. Other possible side effects that constitute a medical emergency, according to MedlinePlus, are nausea, vomiting, hives, itching, unusual bleeding or bruising, and loss of appetite.
  
  

Aspirin

• Aspirin is available in both over-the-counter and prescription forms by itself, and is also combined with prescription pain relievers such as oxycodone to create drugs such as Tylox, according to MedlinePlus. Aspirin can cause Reye's syndrome in children and teenagers, which is a sometimes fatal buildup of fat on the brain and other organs. Other side effects associated with aspirin are nausea, stomachache and heartburn. Serious side effects that are considered a medical emergency include hives, rash, hoarseness, rapid heartbeat, black or bloody stools, and cold, clammy skin.
  
  

Ibuprofen

• Ibuprofen is an over-the-counter and prescription pain reliever and can also be combined with prescription pain relievers like hydrocodone to create drugs like Vicoprofen, according to MedlinePlus. Studies show that those who take ibuprofen may be at a higher risk for having a heart attack or stroke than others in their peer group. Long-term use of the drug can also cause serious stomach problems such as ulcers. Possible general side effects are diarrhea, gas, bloating, constipation, dizziness and nervousness.
  
  

Hydrocodone

• Hydrocodone is a narcotic prescription drug and is not recommended for long-term use due to its addictive potential, according to MedlinePlus. It is combined with non-narcotic pain relievers such as acetaminophen and ibuprofen. Fatal overdose is possible when taking hydrocodone products, which are commonly marketed as Vicodin, Vicoprofen, Norco and Lortab. Other possible side effects are drowsiness, nausea, vomiting, constipation, fuzzy thinking, dizziness, anxiety and an abnormally happy or sad mood.
  
  

Oxycodone

• Oxycodone is a narcotic prescription drug available by itself in medications such as Oxycontin or combined with non-narcotic analgesics such as acetaminophen or aspirin to create medications such as Percocet, Tylox and Percodan, according to MedlinePlus. Addiction and fatal overdose is possible with any form of oxycodone. Other possible side effects include flushing, sweating, itching, red eyes, decreased eye pupil size, weakness, headache and mood changes.