Information should be gathered about the patient and herbal medicine to enable risk assessment and decision making on the interaction.

The importance of asking questions

Asking the right questions and gathering information is important because herbal medicines are known to have interactions and side effects. They should be treated no differently to conventional medicines when it comes to interactions.

NICE advise that complementary medicines should be part of medicines reconciliation and medication reviews.

Refer to our page on understanding complementary medicines.

Gathering information

Take a stepwise approach to gathering information when managing interactions between herbal medicines and conventional medicines.

The following points are intended as a guide and are not exhaustive.

Ask about the reason

Finding out why the person wants to take, or has already started taking, the herbal medicine is important as the answer may identify:

  • sub-therapeutic dosing of a conventional medicine or non-compliance
  • side effects or toxicity from a conventional medicine or another herbal medicine
  • disease progression

Any issues relating to conventional medicines should be resolved before considering a herbal medicine.

Ask about the person

It is possible to identify high-risk patients and high-risk herbal medicines where the advice may be to avoid all herbal medicines.

High-risk patients

The safety of many herbal medicines has not been established in high-risk patients, such as:

  • pregnant women
  • breast-feeding mothers
  • children
  • older people
  • liver disease
  • kidney disease

It is advisable that these people avoid herbal medicines.

High-risk medical conditions

There is a lack of evidence of herbal medicines treating any medical condition. However, some herbal medicines may affect the way in which medical treatments work. This includes treatments for:

  • cancer
  • cardiac disease
  • epilepsy
  • G6PD deficiency
  • HIV

People with high-risk medical conditions should avoid herbal medicines, and herbal medicines should not be used in place of conventional medicines.

Planned surgery

There is limited information on the use of herbal medicines and the risks during surgery and anaesthesia.

The American Society of Anaesthesiology (ASA) recommends that all herbal medication should be stopped for between 2 and 3 weeks before elective surgery. This is a cautious time scale since most herbal medicines do not have a long half-life.

Unplanned surgery

A full medication list is required to identify any herbal medicines. Our herbal interactions resources should be used to decide if any could potentially affect recovery or require closer monitoring of parameters.

For example:

  • ginkgo biloba can affect coagulation
  • valerian can increase sedation
  • echinacea can delay wound healing
  • St John’s Wort can reduce the effects of conventional medicines

Hospital in-patient

Consult your local Trust Medicines Policy regarding the use of herbal medicines by in-patients.

The general advice is that in-patients should not take herbal medicines until they have fully recovered.

Ask about medication

Take a full medication review.

People taking conventional medicines that have a high risk of interactions should avoid herbal medicines. These medicines usually work by:

  • changing protein binding status
  • inducing or inhibiting liver enzymes
  • inducing or inhibiting P-glycoprotein

People taking medicines with a narrow therapeutic index, such as warfarin, should also avoid herbal medicines.

Herbal medicines can interact to enhance side effects of conventional medicines. The BNF lists medicines commonly causing high risk side effects such as hepatoxicity, antiplatelet effects, prolongation of QT interval, sedation, serotonin syndrome, and electrolyte disturbances.

Some herbal medicines can reduce absorption of conventional medicines through effects similar to fibre, such as pectin containing products.

People should be advised either to avoid taking interacting herbal medicines or be counselled on symptom response if they decide to take the herbal medicine.

In some cases, baseline function tests may be required before starting a herbal medicine, such as liver blood tests, kidney function or electrolyte levels.

Ask about herbal medicines

Like conventional medicines, some herbal medicines have a high risk of side effects and interactions. The quality of the unregistered herbal product may also be questionable.

Find out:

Look for excessive dosing of herbal ingredients when people are taking multiple combination products.

High risk examples

Some herbal medicines are known for high-risk side effects or interactions.

For example:

  • ephedra can increase the risk of seizures
  • goldenseal can reduce the effects of metformin
  • ginkgo biloba can increase the risk of bleeding
  • kava can increase the risk of liver damage
  • St Johns Wort can reduce the effect of oral contraceptives

Look at information resources

Use the Summary of Product Characteristics (SmPC) for conventional medicines (accessible via the eMC or MHRA) to understand the likely side effects and interaction mechanisms.

Use the resources for herbal medicines to understand the potential side effects and interaction mechanisms of the herbal medicine.

If one ingredient in a combination herbal medicine interacts with a conventional medicine, there is no need to check the remaining herbal ingredients in the product: the herbal medicine should not be recommended.

Make a decision

During shared decision making on whether or not the herbal medicine should be taken, consider:

  • if the person has a high-risk medical condition
  • if the person is taking a high-risk conventional medicine
  • if the quality of the herbal medicine in doubt
  • if the herbal medicine contraindicated or cautioned with the person’s medical condition
  • if the herbal medicine has any relevant side effects
  • if the herbal medicine has any relevant interactions

If the answer to any of these is yes, advise the person to avoid or stop taking the herbal medicine.

Some herbal medicines may cause withdrawal symptoms or other effects when stopped abruptly. Check the herbal interaction resources for information on the risk of serious withdrawal symptoms from the herbal medicine.

Provide counselling

Where the person decides to take a herbal medicine, advise them to:

  • not stop taking their conventional medicines
  • purchase the herbal medicine from a reputable source
  • take the same brand of herbal medicine (as ingredients can vary for products with the same brand name)
  • take the herbal medicine as stated on the product label
  • not double up on herbal medicines or ingredients
  • report any new or worsening symptoms to their prescriber (including their herbal medicine advisor)
  • include the herbal medicine in their medication list

Healthcare professionals and the public can report any side effects to herbal medicines through the Yellow Card Scheme.

Seek further advice

Contact the SPS Medicines Advice Service when:

  • no information for the herbal medicine can be found
  • the clinical scenario is complex
  • you have doubts and require a second opinion

Print this page