Stockley’s Herbal Medicines Interactions

Stockley’s Herbal Medicines Interactions FAQs

What are herb-drug interactions?

Just like one drug can change the effects of another, herbal medicines can change the effects of a drug, or vice versa. The mechanisms of these interactions sometimes follow that of drug-drug interactions, but at times can differ and be completely unique. Herb-drug interactions are often found incidentally or tested for in experimental or animal studies. This makes it difficult to make robust conclusions on the outcome and severity of any interaction in the clinical setting.

What is Stockley’s Herbal Medicines Interactions?

Stockley’s Herbal Medicines Interactions is a reference source that enables clinicians to manage herb-drug interactions safely and effectively. It gives practical, evidence-based guidance on the interactions between herbal and conventional medicines that is easy to access. It is created by a team of experts in drug interactions with a clinical background and therefore provides practical information on the management of these interactions, enhancing patient safety. In addition to highly structured and rigorously researched interactions monographs, Stockley’s Herbal Medicines Interactions contains herb nomenclature and pharmacopoeial information, as well as details on constituents, common uses, and indications.

Which herbs interact with drugs?

Many herbs have the potential to interact with drugs, and there is no definitive list of which herbal medicines interact with drugs. Stockley’s Herbal Medicines Interactions aims to give the user a comprehensive analysis of over 200 commonly available herbal medicines, nutraceuticals, or dietary supplements and their interactions with conventional drugs.

What is an example of a herb-drug interaction?

One example is the interaction between garlic and warfarin. It has been reported that an increase in anticoagulant effects of warfarin has occurred in some patients taking garlic supplements.

What factors influence drug-herb interactions?

There is significant variability across herbal products. They contain a mixture of many bioactive compounds which makes it hard to predict the extent of their interactions with drugs. Natural products are also liable to a great deal of variation and, even when standardised to one of more of their constituents, there can still be differences in the numerous other compounds present, and different constituents will affect different metabolic enzymes. As well as the source material, the method by which an extract is made will also affect its composition, and thus its interaction potential. For example, different echinacea preparations are known to inhibit the isoenzyme CYP3A4 to varying extents.

What herb-drug combinations should be avoided?

Typically, the herb-drug combinations that should be avoided are those that cause significant harm or where concurrent use is considered to be best avoided. They have often been repeatedly reported in practice and involve high-risk medications, or medications where even small reductions in therapeutic effect are clinically important. One example is the combination of St John’s wort and combined hormonal contraceptives.  Some reports state that St John’s wort had only a minimal effect on the exposure to combined hormonal contraceptives. However, contraceptive failure has been reported in some women. Given the consequences of a reduction in therapeutic effect of these drugs, and the variability of bioactive compounds across herbal products, it is advised that women taking combined hormonal contraceptives should avoid the concurrent use of St John’s wort.

Which herb places the patient at greatest risk of a drug interaction?

Any herb-drug interaction should be evaluated very carefully on a case-by-case basis. The role of Stockley’s Herbal Medicines Interactions is to provide clinicians with evidence-based information about different herbal medicines and their interactions with drugs along with an explanation of the importance and management of any interaction. The clinician can then use this information to guide their actions, which will be individual to any given scenario. The severity of the interaction and the intended benefit should be weighed up, and this will differ from patient to patient.

What do the symbols mean in the interactions monographs in Stockley’s Herbal Medicines Interactions?

The interaction monographs carry an adapted form of the drug interaction. Symbols are used in the Stockley’s Interactions Checker to allow the user to quickly understand the action to be taken for a particular herb-drug interaction. The interactions are rated using three separate categories:

• Action: This describes whether or not any action needs to be taken to accommodate the interaction.
• Severity: This describes the likely effect of an unmanaged interaction on the patient.
• Evidence: This describes the weight of evidence behind the interaction.

These ratings are combined to produce one of five symbols which are displayed in the summary box at the top of each interaction monograph.

How can clinicians access Stockley’s Herbal Medicines Interactions to find out about herbal drug interactions?

Access Stockley’s Herbal Medicines Interactions online via MedicinesComplete. You can contact us for more information about pricing and access information through our sales and upgrade enquiries form.