Herbal Tea and Medication Questions: A Safer Conversation Starter

Herbal teas are pharmacologically active. That is the point of them, and it is also why they can interact with medication. This page is about preparing for a useful conversation rather than diagnosing an interaction yourself.

Why "natural" tells you nothing about safety

Many drugs originate in plants. Being plant-derived says nothing about potency, safety or interaction potential — it describes the source, not the risk.

Herbal products are also regulated less tightly than medicines in most jurisdictions, so concentration can vary between brands and between batches of the same brand.

Interactions worth knowing about

These are examples to raise, not a complete list:

• St John's wort is the significant one. It induces liver enzymes and reduces the effectiveness of many drugs, including hormonal contraceptives, anticoagulants, some antidepressants and antiretrovirals. A 2009 systematic review found clinical-trial evidence that it lowers blood levels of drugs including oral contraceptives and warfarin.
• Liquorice root can raise blood pressure and lower potassium with regular use (a review of liquorice abuse describes both), which matters alongside antihypertensives and diuretics.
• Chamomile and ginkgo have been reported with bleeding in people taking warfarin: a systematic review of warfarin interactions names chamomile tea and Ginkgo biloba among the products to be aware of.
• Grapefruit, appearing in some blends, interacts with a number of medications (see the CMAJ review of grapefruit-medication interactions).
• Ginseng may interact with warfarin and phenelzine, according to a systematic review of herb-drug interactions.
• Green tea is among the products a systematic review lists as affecting warfarin, so it is worth mentioning if you take it.

How to prepare for the conversation

Bring the actual packaging. Ingredient lists on blends are frequently longer than the product name suggests, and the pharmacist needs to see all of it.

Be specific about quantity and frequency. One cup occasionally and four cups daily are different exposures, and this is the detail people most often omit.

List everything you take, including supplements and anything bought over the counter.

Questions worth asking

• Does anything in this blend interact with what I take?
• Does timing help, or is it the total amount?
• Are there signs I should watch for?
• Is there a similar tea without the ingredient of concern?

Who to ask

A pharmacist is usually the most accessible and best-informed source on interactions specifically, and does not require an appointment.

Your prescriber should be involved if a change to medication is being considered.

Do not stop prescribed medication because of something you have read about a herb. Interactions are usually managed by adjusting the herb, not the prescription.

Additional caution

Pregnancy, breastfeeding, liver or kidney conditions, and upcoming surgery all warrant checking before adding unfamiliar botanicals. Surgeons routinely ask about herbal products because several affect bleeding and anaesthesia.