Rituxan can cause severe side effects, including tumor lysis syndrome, a rare brain infection called progressive multifocal leukoencephalopathy, and even death. More commonly, this medication causes digestive issues such as nausea, vomiting, diarrhea, and heartburn. Other common side effects include: soreness in the joints, muscles, or back; overall feelings of weakness and sleepiness; perspiration at night; an increase in weight; flushed skin; a feeling of numbness or a burning or a tingling sensation in your extremities; and a runny nose. Seek immediate medical attention if you experience dizziness, hives, headaches, fits of coughing, impaired vision, swelling at the injection site, odd bruising or bleeding, or difficulty breathing, after receiving a dose of Rituxan. Also seek immediate medical attention if you have any adverse skin reactions, such as ulcers, blisters, sores on your skin or mouth, or a severe rash. These reactions may indicate something serious and ultimately can lead to death.