Interactions between herbal medicines and prescribed drugs: a systematic review.
Level 1 - systematic review of randomized trials
Systematic review of human studies (clinical trials and case reports/series)
PubMed 11772128 · doi:10.2165/00003495-200161150-00002
What was done
The authors conducted a systematic review searching Medline, the Cochrane Library, Embase, and Phytobase from database inception to July 2000 to identify human data on drug interactions involving the top seven selling herbal medicines: ginkgo, St John's wort, ginseng, garlic, echinacea, saw palmetto, and kava. All human study designs (clinical trials, case reports, and case series) were included, while in vitro studies were excluded. Data extraction was conducted by one author and validated by a second.
What was found
The review identified 58 publications, comprising 41 case reports or case series and 17 clinical trials. The abstract reports qualitative clinical outcomes and directions of effect without numerical values: - St John's wort lowered blood concentrations of cyclosporin, amitriptyline, digoxin, indinavir, warfarin, phenprocoumon, and theophylline; it was associated with intermenstrual bleeding when combined with oral contraceptives, delirium with loperamide, and mild serotonin syndrome with SSRIs (sertraline, paroxetine, nefazodone). - Ginkgo was associated with bleeding when combined with warfarin, elevated blood pressure with thiazide diuretics, and coma with trazodone. - Ginseng lowered blood concentrations of alcohol and warfarin, and induced mania when combined with phenelzine. - Garlic altered paracetamol pharmacokinetics, decreased warfarin blood concentrations, and produced hypoglycemia with chlorpropamide. - Kava increased 'off' periods in Parkinson patients taking levodopa and caused a semicomatose state with alprazolam. - No interactions were found for echinacea or saw palmetto.
Why it matters
This review establishes that widely used herbal medicines can cause clinically significant pharmacokinetic and pharmacodynamic interactions with critical medications, including anticoagulants, immunosuppressants, and antiretrovirals.
Limits
The abstract provides no numerical data, effect sizes, or confidence intervals. The majority of included evidence (41 of 58 publications) consists of anecdotal case reports or case series rather than controlled clinical trials.
Cited by
- supports Combining St. John's wort with an SSRI medication can adversely interfere with serotonin levels.