Interactions between herbal medicines and prescribed drugs: a systematic review

source extracted confidence: high 2026-04-09
#drug-interactions #drug-prescriptions #echinacea #garlic #ginkgo-biloba

Interactions between herbal medicines and prescribed drugs: a systematic review

Izzo et al., 2001 | Drugs | Systematic Review

Citation

Izzo A A, Ernst E. Interactions between herbal medicines and prescribed drugs: a systematic review. Drugs. 2001;61(15):2163-75

Abstract

Despite the widespread use of herbal medicines, documented herb-drug interactions are sparse. We have reviewed the literature to determine the possible interactions between the seven top-selling herbal medicines (ginkgo, St John's wort, ginseng, garlic, echinacea, saw palmetto and kava) and prescribed drugs. Literature searches were performed using the following databases: Medline (via Pubmed), Cochrane Library, Embase and phytobase (all from their inception to July 2000). All data relating to herb-drug interactions were included regardless of whether they were based on case reports, case series, clinical trials or other types of investigation in humans. In vitro experiments were excluded. Data were extracted by the first author and validated by the second author. 41 case reports or case series and 17 clinical trials were identified. The results indicate that St John's wort (Hypericum perforatum) lowers blood concentrations of cyclosporin, amitriptyline, digoxin, indinavir, warfarin, phenprocoumon and theophylline; furthermore it causes intermenstrual bleeding, delirium or mild serotonin syndrome, respectively, when used concomitantly with oral contraceptives (ethinylestradiol/desogestrel), loperamide or selective serotonin-reuptake inhibitors (sertaline, paroxetine, nefazodone). Ginkgo (Ginkgo biloba) interactions include bleeding when combined with warfarin, raised blood pressure when combined with a thiazide diuretic and coma when combined with trazodone. Ginseng (Panax ginseng) lowers blood concentrations of alcohol and warfarin, and induces mania if used concomitantly with phenelzine. Garlic (Allium sativum) changes pharmacokinetic variables of paracetamol, decreases blood concentrations of warfarin and produces hypoglycaemia when taken with chlorpropamide. Kava (Piper methysticum) increases 'off' periods in Parkinson patients taking levodopa and can cause a semicomatose state when given concomitantly with alprazolam. No interactions were found for echinacea (Echinacea angustifolia, E. purpurea, E. pallida) and saw palmetto (Serenoa repens). In conclusion, interactions between herbal medicines and synthetic drugs exist and can have serious clinical consequences. Healthcare professionals should ask their patients about the use of herbal products and consider the possibility of herb-drug interactions.

Key Findings

Healthcare professionals should ask their patients about the use of herbal products and consider the possibility of herb-drug interactions.

Outcomes Measured

  • blood pressure

Population

Field Value
Population See abstract
Sample Size See abstract
Age Range See abstract
Condition blood pressure

MeSH Terms

  • Drug Interactions
  • Drug Prescriptions
  • Echinacea
  • Garlic
  • Ginkgo biloba
  • Herb-Drug Interactions
  • Humans
  • Hypericum
  • Kava
  • Panax
  • Phytotherapy
  • Plant Extracts
  • Plant Preparations
  • Serenoa

Evidence Classification

  • Level: Systematic Review
  • Publication Types: Journal Article, Systematic Review
  • Vertical: garlic

Provenance

  • PMID: 11772128
  • DOI: (not available)
  • PMCID: Not in PMC
  • Verified: 2026-04-09 via PubMed E-utilities API

Source extracted via PubMed E-utilities API on 2026-04-09