Granisetron can cause a serious heart problem, especially if you use certain medicines at the same time, including antibiotics, antidepressants, heart rhythm medicine, antipsychotic medicines, and medicines to treat cancer, malaria, HIV or AIDS.
Taking granisetron together with certain other medicines can cause high levels of serotonin to build up in your body, a condition called "serotonin syndrome," which can be fatal. Tell your doctor if you also use:
lithium;
ritonavir;
St. John's wort;
an antidepressant;
migraine headache medicine;
a narcotic (opioid) medication or muscle relaxer; or
other anti-nausea medications.
This list is not complete. Other drugs may interact with granisetron, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide. Tell your doctor about all medicines you use, and those you start or stop using during your treatment with granisetron.
 Granisetron drug interactions (more detail)
