What should you know about prophylactic Tamiflu?

Oseltamivir works against influenza viruses by interfering with their ability to spread in the body. A clinician may consider it for someone at increased risk of complications, including some people receiving cancer treatment, or after close contact with a person who has influenza. The decision depends on timing, symptoms, kidney function, other medicines, local influenza activity, and the possibility of an alternative diagnosis.

Preventive treatment does not replace seasonal vaccination, hand hygiene, or avoiding close contact when someone is ill. It also does not treat every cough or fever. Do not share capsules or start leftover medicine without advice.

Tell the prescriber about chemotherapy, immunotherapy, steroid treatment, kidney problems, allergies, pregnancy, and all medicines or supplements. Take the medicine exactly as directed and ask what to do after a missed dose. Nausea, vomiting, headache, and stomach upset can occur; reporting troublesome effects helps the team decide whether the plan needs adjustment.

If you develop influenza-like symptoms, call the oncology or primary-care team promptly because treatment timing may differ from prevention. Ask whether you need testing, isolation guidance, or a review of your cancer treatment schedule. Related reading includes [Hormone Therapy for Cancer](/treatments/systemic-therapy/hormone-therapy-for-cancer/) and [Risk-Reducing Endocrine Therapy](/treatments/risk-reduction-and-prevention/risk-reducing-endocrine-therapy/).

Contact a clinician promptly for fever, worsening cough, shortness of breath, chest pain, dehydration, persistent vomiting, confusion, or marked weakness. Seek emergency care for severe breathing difficulty, bluish lips, collapse, or new confusion. People receiving cancer treatment may need an urgent assessment even when symptoms initially seem mild.

Why is prevention being considered for me? When should I start and stop it? What symptoms mean I should be tested or treated rather than continuing prevention? Could it interact with my cancer medicines or kidney function?