Nausea and Vomiting in Cancer Patients People may experience nausea and vomiting for many reasons.  In people with cancer, for example, causes include the cancer itself, the treatments, or additional factors such as infections or other diseases and illnesses.  One of the main causes of nausea and vomiting in people with cancer is chemotherapy. The specific chemotherapy drug used, the level of dose required, its frequency, and how it is given, may all influence the development of nausea and vomiting.  Another influencing factor may be how well a patient tolerates chemotherapy and other medications.  A patient’s overall health can also play a role. Chemotherapy does not cause nausea and vomiting in everyone.  However, many people with cancer do experience these side effects.