Herbal teas might look harmless, but some can interfere with chemotherapy. Some teas can change how your body absorbs or breaks down medicine, raise the risk of bleeding, or affect liver enzymes. This could make your treatment less effective or cause more side effects. Not every tea is unsafe, but it’s important to let your cancer care team know about any herbal teas or supplements you use. If you’re unsure, plain black or green tea in small amounts is usually safer than strong herbal blends.