Drug, Food and Supplement — Interactions With Alectinib

No. Grapefruit juice blocks the enzyme your liver uses to clear alectinib, causing it to build up to higher levels than intended. Higher levels increase the risk of side effects without adding any extra benefit to your treatment. This applies to fresh grapefruit, bottled grapefruit juice, and any product that contains grapefruit. Oranges, lemons, limes, and other citrus fruits are fine.

No. St. John's Wort activates the liver enzyme that clears alectinib, causing the drug to be broken down faster than intended. This can reduce alectinib to levels where it is no longer effective against the cancer. If you have been taking it, tell your oncologist — do not simply stop without mentioning it, because the team will want to know how long you have been using it and review your treatment response in that context.

No, but contact your oncology team the same day. Clarithromycin blocks the enzyme that clears alectinib, which causes alectinib to build up. An alternative antibiotic — amoxicillin, for example — usually works just as well for chest and sinus infections and does not carry this interaction. Your GP can switch the prescription once the team has confirmed the alternative is appropriate for your infection.

Do not change or stop your epilepsy medicine without speaking to both your neurologist and your oncologist first. Stopping anti-epileptic medicines suddenly can trigger seizures, which is a serious risk in its own right. Some epilepsy medicines do reduce alectinib levels, but managing this safely is a conversation between specialists — not something to act on alone. An alternative anti-epileptic with less interaction may be available.

Antifungal creams and pessaries applied to the skin or used vaginally are absorbed very little into the bloodstream and are not generally considered to interact with alectinib in a meaningful way. Oral antifungal tablets — ketoconazole, itraconazole, voriconazole, posaconazole — are the concern. If you are prescribed antifungal tablets for any reason, tell your oncology team before starting them.

Herbal and traditional preparations can interact with alectinib in the same way that pharmaceutical medicines do, because the active plant compounds they contain affect the same liver enzymes. This is not a reason to stop taking them without talking to your team first — but it is a reason to bring everything you are taking to your next appointment, including supplements, tonics, and anything given by a traditional practitioner. Your oncologist will tell you which ones need closer review.

Paracetamol at standard doses is generally considered the safer choice for mild pain or fever while on alectinib. Ibuprofen and other anti-inflammatory pain medicines carry their own risk to the liver and kidneys, and alectinib can cause liver enzyme changes — so ask your oncology team before using ibuprofen regularly. For any pain that is new or getting worse, contact the team rather than managing it with over-the-counter medicines.

Contact your oncology team before starting anything new — prescription medicines, over-the-counter medicines, supplements, and herbal preparations. Give them the name of the medicine and the dose. If it is urgent and you cannot reach the team, a pharmacist at your treatment centre is usually the fastest resource. In any emergency where another doctor is prescribing for you, make sure they know you are on alectinib by name — not just 'a cancer tablet' — so they can check the interaction before prescribing.