Herb drug interactions

Many medicinal herbs and pharmaceutical drugs are therapeutic at one dose and toxic at another. Interactions between herbs and drugs may increase or decrease the pharmacological or toxic effects of either. Although there are very few reports of adverse herb-drug interactions there are circumstances in which certain herbs should be avoided.

Examples of these combinations are given below, but it must be stressed that this list is not exhaustive. If in doubt, consult a qualified herbal proctitioner or your GP.

Garlic(Allium sativum)and Ginkgo (Ginkgo biloba) should be avoided when taking blood thinners such as warfarin, as they too act to thin the blood.

St John’s Wort should not be take in conjuction with the oral contraceptive pill as it can reduce its effectiveness and therefore increase the risk of pregnancy.

Ephedra (Ephedra sinica) should avoided when taking certain types of antidepressant (MAOIs) as the combination can lead to high blood pressure.

Contraindications for herbs

Not all herbs are suitable for everyone and should not be taken when suffering from certain conditions. Examples are given below but again, please not that this list is not exhaustive.

Liquorice (Glycerrhiza glabra) should be avoided with high blood pressure as this can cause an increase in blood pressure.

Juniper (Juniperus communis ) should not be used where there is kidney disease as it contains a volatile oil which irritates the kidneys.

Black cohosh (Cimicifuga racemosa) should not be used in breast cancer (an oestrogen-dependent tumour) as it contains constituents that mimic the effects of oestrogen.

Willow (Salix spp.) should be avoided by those who are allergic to aspirin as it contains salicylates which are a natural form of the drug.

Some herbs are more toxic that others and must be used with caution and in small doses. These should not be used except under the guidance of a qualified herbal practitioner.

Examples of such herbs include:

Pregnancy

Although many herbs are safe to use when pregnant or breastfeeding, there a quite a number that should be avoided. These include herbs with a hormonal effect such as sage, or herbs with a strong irritant or laxative effect such as senna or yellow dock.

During pregnancy it is advisable to take herbal medicines, as with any medicine, only when really necessary. It is preferable to take no medication during the first three months of pregnancy. If in doubt, consult a qualified herbal practitioner.

Children

The majority of herbs are safe to give children, although the dose given is reduced according to the age and size of the child. Some herbs, such as peppermint, are best avoided for those under 12 years of age.

Over-The-Counter Products

Many over the counter products are produced by reputable companies and are safe and effective. However, as the area is not yet regulated this cannot be guaranteed. Indeed some products when analysed have been found to contain nothing but ash! When looking for over-the-counter products there are certain things you can do to try to ensure you are buying a good quality product.

Buy your remedies from a reputable and knowledgeable supplier who can give clear advice about the product. Ask what training the assistant has had. Be wary if they have only had training from the product supplier.

Beware of very cheap products – they may be cheap for a very good reason.

Dried herbs should be carefully stored out of the light in a dry place. They should not be kept for longer than one year as they lose their effectiveness over time. Good quality herbs will have a distinct smell and taste.

Products should show the manufacturers name and contact details.

The product label should list the ingredients and give the recommended dose. For tablets or capsules the individual weight should be given. For tinctures, the ratio of herb to liquid should be given (eg. 1:5).

Try to buy organic products as they will contain fewer unwanted chemicals and will not have been irradiated.

However, one of the main dangers of self-treatment is missing or masking a potentially serious condition. If in doubt, always seek the advice of a qualified herbalist or you GP.