Supplement and Herb Interactions With Medicines and Surgery: Why Disclosure Matters

Herbs and supplements can act like medicines in the body. That is why every clinician, and any naturopath or other practitioner you see, needs the full list of what you take. This page is information only. Do not stop or change a prescribed medicine on your own; ask the prescriber.

Why disclosure matters

NCCIH says dietary supplements may interact with your medications or pose risks if you have certain medical problems or are going to have surgery. [1] Examples it gives: St. John's wort makes many medications less effective, and kava supplements can cause liver disease. [1] It also warns that "natural" does not always mean "safe." [1]

Product contents can differ from the label. NCCIH reports that the FDA has found prescription drugs, including the anticoagulant warfarin and the anticonvulsant phenytoin, in products sold as dietary supplements. [1] The FDA is not authorized to review most supplements for safety and effectiveness before they are marketed. [1] See how supplements are regulated and product quality and contamination.

Medicines named by the NHS

The NHS (UK) lists medicines that do not mix well with herbal medicines: statins, antidepressants, diabetes medicines such as metformin, blood pressure medicines such as ramipril, blood thinners such as warfarin, and hormonal contraception such as the combined pill. Together they may cause harmful effects or stop your medicine working. [2] It advises checking with a pharmacist before taking a herbal medicine if you already take other medicines, including ones bought without a prescription. [2] For more on how interactions work see interactions by drug class and how interactions work.

Before surgery

The American Society of Anesthesiologists (ASA) says some supplements can prolong the effects of anesthesia, increase bleeding, raise blood pressure, interfere with other medications or cause heart problems. [3] Its leaflet gives these examples:

[3]

The ASA says to bring all your medication and supplement bottles to your pre-surgery visit, and that your physician anesthesiologist may recommend stopping supplements at least two weeks before the procedure. [3] It also says studies show half of people who use herbal supplements do not tell their doctors before surgery. [3] NCCIH likewise says to talk to your providers as far in advance as possible and to tell them about all the supplements you take. [1] Follow your surgical team's instructions on timing; do not decide alone. See supplements before surgery.

During cancer treatment

NCCIH says some herbs may make chemotherapy drugs less effective, and the effects of vitamin and mineral supplements, including antioxidants, during cancer treatment are uncertain; discuss them with your providers. [4] In a breast cancer trial analysis, use of antioxidant supplements during chemotherapy was associated with a possibly higher hazard of recurrence (borderline statistical significance), and vitamin B12 and iron use with poorer outcomes. [5] That was observational, so it shows association only.

How strong is the evidence?

The sources above are guidance from medical and government bodies and one observational study. We did not grade each herb and medicine pair. Proper evidence not found, in the sources we read, for a single graded list covering all combinations, so ask a pharmacist about your exact products.

What to do

• Keep a written list of every medicine, supplement, herb, tea and oil, with doses as printed on the label.
• Show it to each clinician and pharmacist, including a naturopath if you see one. See medication and supplement review.
• If a practitioner dispenses products, ask what is in them and whether they interact with your medicines.
• Report side effects. NCCIH says if you have side effects, stop the supplement and contact your health care provider. [1]