Both Tylenol and Aleve provide pain relief and lower fever. Tylenol is acetaminophen and Aleve is a nonsteroidal anti-inflammatory. Taking Tylenol according to recommended dosage produces negligible adverse effects. Aleve, however, causes many side effects. When taken together, Tylenol and Aleve can lead to serious side effects. Although rare, these adverse reactions can be fatal.
According to "Pearson Nurse's Drug Guide 2010," Aleve can take three to four weeks to reach full therapeutic effect. Tylenol provides noticeable relief within 30 minutes of ingestion. Taking Tylenol with Aleve provides pain relief during this interim. Because these two medications work to relieve pain in different ways, mixing Tylenol and Aleve produces more comprehensive pain relief.
Prolonged use of Tylenol or Aleve causes low white blood cell counts. The National Institute of Health reports this rare but potentially fatal side effect occurs in fewer than 1 percent of users. However, combining the drugs together increases the incidence of this adverse effect. Low white blood cell levels increases a person's risk for infection. Patients taking Aleve and Tylenol together require regular blood tests to monitor for this complication.
Both Tylenol and Aleve lower platelet production when taken for a long period of time. Platelets are necessary for proper blood clotting, and low platelet counts lead to easy bruising and bleeding. Mixing Tylenol and Aleve causes a rapid and more pronounced drop in platelet production, and can be lethal. Patients should be monitored for blood loss and have regular check-ups with a doctor.
Overdose or long-term use of Tylenol damages the liver. The liver metabolizes both Tylenol and Aleve, so people who take Tylenol and Aleve together for a prolonged period of time have an increased risk of developing liver toxicity. Liver toxicity causes nausea, abdominal pain, elevated liver enzymes and yellow discoloration of the skin. Patients should report such symptoms to the doctor and have routine blood work to monitor for this lethal side effect.
Another side effect of mixing Tylenol and Aleve is renal failure. This complication occurs because both drugs are excreted in the urine after being filtered by the kidneys. The exacerbating factor is prolonged use. Patients who take Tylenol and Aleve together for chronic pain should have regular lab work to assess kidney function.