Tylenol, also known as acetaminophen, is a common over-the-counter medication used to treat pain and reduce fever. While Tylenol is generally considered safe when used as directed, it can cause side effects, especially when taken in large doses or in combination with other medications. Here are some potential side effects of Tylenol:

1. Liver damage: One of the most serious side effects of Tylenol is liver damage. This can occur when taking large doses of Tylenol or when taking it for an extended period of time. Symptoms of liver damage may include nausea, vomiting, and abdominal pain. In severe cases, liver failure can occur.
2. Stomach pain: Tylenol can cause stomach pain, especially when taken on an empty stomach.
3. Rash: Some people may develop a rash after taking Tylenol.
4. Allergic reaction: In rare cases, Tylenol can cause an allergic reaction. Symptoms of an allergic reaction may include hives, swelling of the face or throat, and difficulty breathing.
5. Blood disorders: Tylenol can cause blood disorders, such as thrombocytopenia (a condition in which the blood has a lower than normal number of blood cell fragments called platelets) and leukopenia (a condition in which the number of white blood cells in the blood is below normal).

It is important to note that Tylenol can interact with other medications, including some prescription drugs, over-the-counter medications, and herbal supplements. Therefore, it is important to speak with a healthcare provider before taking Tylenol if you are taking any other medications.

Sources:

1. Mayo Clinic. (2021). Acetaminophen (Oral Route) Side Effects. Retrieved from <https://www.mayoclinic.org/drugs-supplements/acetaminophen-oral-route/side-effects/drg-20068783?p=1>
2. DrugPatentWatch. (2021). Tylenol. Retrieved from <https://www.drugpatentwatch.com/drugs/tylenol>
3. U.S. Food and Drug Administration. (2021). Acetaminophen Information. Retrieved from <https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/acetaminophen-information>