Interactions between herbal remedies and other medicines
According to a review on the use of herbal remedies by patients with cardiovascular diseases, published in February 2010 in the Journal of the American College of Cardiology by physicians from the Mayo Clinic (reference below), consultations with practitioners of complementary and alternative therapies account for $30 billion spending per year in the USA and more visits are paid to these practitioners than to primary care physicians. Herbal remedies are one of the most popular forms of alternative medicine.
Moreover, very many herbal remedies are freely available for purchase and thus are widely consumed as self-medication without prior consultation. The Mayo paper claims that herbal remedies and high-dose vitamin supplements are used by more than 15 million people in the USA, with herbal remedies forming the bulk of this use.
At present, herbal remedies do not have to go through the years of testing required by the FDA (US Food and Drug Administration) for pharmaceuticals. On the other hand, the regulations require them to be marketed as dietary supplements and no claims concerning curative properties or other health benefits can be made on the packaging or in advertising. Partly for this reason, many not only see herbal remedies as being “gentler” than synthetic medicines, but also do not feel it necessary to tell their physician that they are using herbal remedies.
Herbal remedies can have as potent pharmacological effects as any conventional medicine. They can interact with medicines to produce unexpected, and even dangerous, effects.
This article summarises some of the interactions that can occur between six popular herbal remedies (St John’s Wort, Ginkgo biloba, ginseng, echinacea, valerian, evening primrose) and other medicines.
St John's Wort
St John’s wort is widely used for depression, sleep disorders and anxiety and indeed has been shown in some studies to be as effective as some antidepressants.
However, St John’s wort can interact with a very large number of medicines.
Interactions that make other medicines less effective
In many cases, this herb competes with other medicines and lowers their concentration in the blood, thus making them less effective. Examples of such interactions include:
- antihistamines (Allegra, Zyrtec, Claritin)
- immunosuppressants such as cyclosporine, methotrexate, tacrolimus and azothiprine. These drugs are used in autoimmune diseases such as lupus, and when taken together with St John’s wort may not be effective enough to control the symptoms. Immunosuppressants are also given to transplant recipients. The effect of St John’s wort could lower the levels of the immunosuppressant to such a degree that it can no longer prevent the transplanted organ being rejected.
- cardiovascular drugs such as digoxin (Lanoxin), reserpine and some calcium channel blockers (both used to lower high blood pressure), statins (cholesterol-lowering drugs), warfarin (blood-thinner)
- contraceptive pills are potentially made less effective, since there have been reports of women having breakthrough bleeding when taking St John’s wort at the same time
- drugs against HIV and AID: protease inhibitors and non-nucleoside reverse transcriptase inhibitors
- theophylline (used to help breathing in chronic bronchitis, emphysema and severe asthma)
Interactions that increase side effects of other medicines
In other cases, St John’s wort increases the activity of medicines or mimics some of their activity, thus increasing the frequency and severity of side effects. These medicines include:
Serotonin syndrome is due to an excess of serotonin in the body. In severe cases, symptoms include high blood pressure, fever, convulsions and confusion. The condition can progress to coma and death. Immediate medical help is needed if serotonin syndrome is suspected.
- Antidepressants: SSRIs (e.g. Celexa, Prozac, Zoloft, Paxil), tricyclic antidepressants (e.g. amitryptyline, imipramine) and MAO inhibitors. Not only are side effects increased, but there is a danger of serotonin syndrome developing.
- Dextromethorphan is found in many over-the-counter cough and cold medicines. As well as an increase in side effects, there is a danger of serotonin syndrome.
- Migraine medication (triptans): As well as an increase in side effects, there is a danger of serotonin syndrome.
- Sleeping pills, anticonvulsants (e.g. valproic acid, phenytoin), barbiturates and benzodiazepines (Valium, Xanax) all have their sedative effect increased by St John’s wort. This can lead to potentially fatal respiratory depression.
Ginkgo is particularly popular as an herbal remedy to prevent or treat dementia, memory loss and other cognitive decline. The benefit of ginkgo biloba supplements has been demonstrated in a number of conditions and diseases.
- Ginkgo decreases the “stickiness” of blood platelets and thus increases the risk of bleeding. It is therefore potentially dangerous to take ginkgo together with medicines that increase the risk of bleeding, such as aspirin, "blood thinners" (anticoagulants) e.g. heparin and warfarin, non-steroidal anti-inflammatory drugs (ibuprofen, naproxen) anti-platelet drugs e.g. clopidogrel (Plavix).
- Because ginkgo is thought to influence blood levels of sugar and insulin, it may potentially be dangerous when taken with antidiabetic drugs and insulin.
- Ginkgo taken in high doses may possibly make some anticonvulsants, such as carbamazepine and valproic acid, less effective.
- Theoretically, ginkgo could increase the side effects of MAO inhibitors and SSRIs and possibly increase the risk of serotonin syndrome. However, this suspicion is based on animal studies and there have been no reports of such incidents in humans.
Ginseng is used as a general tonic, aphrodisiac, and also to boost the immune system and resistance.
Siberian ginseng (Acanthopanax senticosus, Eleutherococcus senticosus) can increase the side effects of digoxin and some sedatives, especially barbiturates.
American ginseng (Panax quinquefolium) and Asian ginseng (Panax ginseng) can:
- lower blood sugar levels and therefore be potentially be dangerous when taken with antidiabetic drugs and insulin
- further increase the risk of bleeding when taken with medicines that increase the risk of bleeding, such as aspirin, heparin, non-steroidal anti-inflammatory drugs (ibuprofen, naproxen) anti-platelet drugs e.g. clopidogrel (Plavix). Paradoxically, though, it decreases the anticoagulant efficacy of warfarin by lowering levels of warfarin in the blood.
- increase the side effects of MAO inhibitors
- alter the effects of medicines taken for heart disease or high blood pressure
- possibly block the pain-relieving activity of morphine
Evening primrose oil is widely used to treat skin problems and for female problems such as premenstrual tension, menopausal symptoms and breast tenderness during the menstrual cycle.
It is thought to decrease the seizure threshold, and therefore will increase the risk of seizures associated with phenothiazine drugs (e.g. chlorpromazine, perphenazine, thioridazine), which are used to treat schizophrenia.
Because of its effect on the seizure threshold, evening primrose oil may cause an established dose of an anti-epileptic drug to be less effective in preventing seizures.
Echinacea stimulates the immune system. It will therefore block the activity of immunosuppressants such as cyclosporine, methotrexate, tacrolimus and azothiprine used in autoimmune diseases and after organ transplantation.
Valerian is used to help sleep and for its calming effect.
As a sedative itself, valerian will increase the sedative effects of sleeping pills, anticonvulsants (e.g. valproic acid, phenytoin), barbiturates and benzodiazepines (Valium, Xanax). This can lead to potentially fatal respiratory depression. Likewise, it may increase the effects of general anaesthesia if used shortly before surgery.
These are just some of the interactions that can occur between popular herbal remedies and other medicines. If you intend to take a herbal remedy and you are on other medication, you should always ask your doctor or pharmacist for advice before starting. Likewise, if you regularly use a herbal remedy, you should tell your doctor this when you receive a prescription for a new medicine.
This article was based primarily on information from the following resources:
Complementary and Alternative Medicine Index, University of Maryland Medical Centre
Ara Tachjian, Viqar Maria, and Arshad Jahangir
Use of Herbal Products and Potential Interactions in Patients With Cardiovascular Diseases
J Am Coll Cardiol, 2010; 55:515-525
St John’s Wort by Igor Savin (Игоревич); Ginseng by Richardfabi; Echinacea by RI on Wiki Commons
Ginkgo biloba plant by Marcefabi at http://www.arteyfotografia.com.ar/3111/fotos/
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