Herbal products drug interactions

Tirana RG, Bailey DG. Herbal product - drug interactions mediated by induction. Br J Clin Pharmacol 2006 61 677-681. 

Tirona, R. G. and Bailey, D. G. (2006) Herbal product-drug interactions mediated by induction. Br. J. Clin. Pharmacol. 61, 677-681. 

However, the information derived from a detailed pharmacokinetic study will help to anticipate potential botanical product-drug interactions, to optimize the bioavailability, the quality, and hence the efficacy of herbal medicines, to support evidence for the synergistic nature of herbal medicines, and to better appreciate the safety and toxicity of the plant. Because pharmacokinetic studies with herbal medicines are often complicated by their chemical complexity and by the fact that the active compounds are often unknown, it could be one future issue to assess bioavailability by measuring surrogate parameters in plasma or tissue instead of directly assaying putative active compounds in the blood. In summary, to use HMPs in an evidence-based approach and to achieve the status rational phytomedicine, more experimental studies are needed to characterize the bioavailability and pharmacokinetics of botanical products. 

Chen S. Development of herbal products as pharmaceutical agents—new regulatory approaches and review process at U.S. FDA. In Lam YW, Huang S-M, Hall SD, eds. Herbal Supplements—Drug Interactions. Taylor Francis, 2006. 

St. John s wort This herbal remedy may induce CYP3A4 the certainty of an interaction probably rests on the specific preparation being used, but caution would dictate that this herbal product should be avoided in those receiving methadone treatment withdrawal symptoms have been noted in patients taking methadone maintenance who have added St. John s wort to their drug regimen. 

Black cohosh has been one of the most studied herbal remedies for vasomotor symptoms, and it has not demonstrated a substantial benefit over placebo. The mechanism of action, safety profile, drug-drug interactions, and adverse effects of black cohosh remain unknown. In non-placebo-controlled trials conducted for 6 months or less, black cohosh demonstrated a small reduction in vasomotor symptoms. It has not been shown to be effective for vasomotor symptoms in women with breast cancer.33 There have been case reports of hepatotoxicity with the use of black cohosh.36 Caution should be exercised when considering the use of this product, especially in patients with liver dysfunction. 

To make a rational decision about a herbal product, it would be necessary to know what it contains, whether it is safe, how it interacts with drugs or other herbs, and whether it has been demonstrated to be as good or better than pharmaceutical products available for the same purpose. For most herbal ingredients this information is incomplete or unavailable. 

This herbal product has the most data available to support its usefulness as an antidepressant. Nevertheless, only minimal information is available about its pharmacology and its relative risk-benefit ratio. At least seven different biologically active chemicals have been isolated from crude extracts of hypericum. Several are ubiquitous in the plant kingdom. The exceptions are hypericin and pseudohypericin, which have been assumed to be responsible for any antidepressant activity of this product. Nevertheless, there is the potential for one or more of these seven compounds and their metabolites to mediate desired or undesired effects, particularly when used in combination with other medications (i.e., herb-drug interactions). 

Huang SM, Hall SD, Watkins P, et al. Drug interactions with herbal products and grapefruit juice a conference report. Clin Pharmacol Ther 2004 75(1) 1-12. 

ALESSE 28 (levonorgestrel and ethinyl estradiol tablets) Wyeth April 2004 labeling Precautions. Drug Interactions Herbal products containing St. John s wort H. perforatum) may induce hepatic enzymes (CYP) and P-gp transporter and may reduce the effectiveness of contraceptive steroids. This may also result in breakthrough bleeding ... 

Table 4.6 Factors complicating assessment of drug interactions with herbal products...

Herbal medicines are becoming more and more popular, and indeed some herbal products may be considered to benefit people with liver disease, e.g. Silybum marianum (milk thistle), Picrorhiza kurroa, Phyllanthus, etc. Herbal hepatotoxicity is increasingly being recognised, for example, with kava kava, black cohosh, and many traditional Chinese remedies. The range of liver injury includes minor transaminase elevations, acute and chronic hepatitis, steatosis, cholestasis, zonal or diffuse hepatic necrosis, veno-occlusive disease and acute liver failure. In addition to the potential for hepatotoxicity, herb-drug interactions may affect the safety and efficacy of concurrent medical therapy [15]. 

In 2006, a survey in Italy revealed that herbal products were taken in combination with drugs by nearly 45% of the population. The information provided was derived from a multitude of sources that described interactions in the form of case reports, animal studies and, rarely, human volunteer studies. 

In 2009, in the UK, drugs are increasingly available over the counter and on-line without prescription. Furthermore, there is widespread use of numerous herbal medicines from relatively under-regulated suppliers and the constituents of such products are often not known, This clinical reality of the widespread use of potent medicines - be they allopathic or traditional - showed us the need for a practical hands-on guide that aims to be a compact, succinct and accessible source of information for practitioners, prescribers and the public about adverse drug interactions,... 

Patients should be aware that health care practitioners cannot guarantee the safety and consistency of herbal products. Patients should start with the recommended effective doses and report any unusual side effects to their health care practitioner. Patients should always consult with their pharmacist for possible drug-herbal interactions. Side effects and possible drug interactions for the ten most commonly used herbals are listed in Table 7. 

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