Topic Overview

Most people recover from mononucleosis (mono) without any complications. But there are many possible complications of mono. These include:

• An enlarged spleen, which occurs in up to 75 out of 100 people who have mono.^{footnote 1}
• Red spots or rash, which can develop if you are taking certain antibiotics. The rash is not an allergic reaction.^{footnote 2}
• Mild anemia, which usually goes away without treatment after 1 to 2 months.
• White blood cells (lymphocytes) that look abnormal may result from a mononucleosis infection.
• Mild hepatitis, which usually goes away on its own without treatment.

Other complications of mono can occur but are very rare. These include:

• A ruptured spleen. To reduce the risk for this problem, avoid contact sports and heavy lifting for 4 weeks after you become ill. It can be the first sign of mono in a small number of people. A ruptured spleen requires immediate surgery.
• Airway obstruction and difficulty breathing, which may be caused by severely swollen tonsils that block the throat. Corticosteroids may be given to reduce swelling. In severe cases, the tonsils may need to be removed surgically (tonsillectomy).
• Brain and spinal cord problems.
• Cardiac problems, such as irregular heart rhythms, which can occur during the first 3 weeks of mono. These types of problems usually resolve on their own.

While it is not a complication specific to mono, a serious disease known as Reye syndrome can develop if you give aspirin to a person younger than 20 to treat symptoms of mono. Aspirin should not be used to treat symptoms of mono. Other medicines, such as acetaminophen (for example, Tylenol) or ibuprofen (for example, Advil) can help relieve fever and pain caused by mono. Be safe with medicines. Read and follow all instructions on the label.

Even if you have a complication of mono, it is likely that you will recover completely.