Potential interactions between conventional medications and herbal products.
Overview
Herbal supplements are widely used but can interact with prescription medications. These interactions are often underreported and may be clinically significant.
High-Risk Herbs
St. John's Wort (Hypericum perforatum)
One of the most problematic herbs for drug interactions.
Drug Class
Effect
Severity
SSRIs
Serotonin syndrome risk
Serious
Oral contraceptives
Reduced efficacy
Serious
Cyclosporine
Reduced levels
Serious
HIV medications
Reduced efficacy
Critical
Warfarin
Reduced anticoagulation
Serious
Digoxin
Reduced levels
Serious
Mechanism: Potent inducer of CYP3A4 and P-glycoprotein
Ginkgo Biloba
Drug Class
Effect
Severity
Anticoagulants
Increased bleeding
Moderate
Antiplatelet agents
Increased bleeding
Moderate
Seizure medications
May lower threshold
Moderate
Garlic Supplements
Drug
Effect
Severity
Warfarin
Increased bleeding risk
Moderate
HIV protease inhibitors
Reduced levels
Moderate
Antiplatelet drugs
Additive effects
Moderate
Ginseng
Drug
Effect
Severity
Warfarin
May decrease INR
Moderate
Diabetes medications
Hypoglycaemia risk
Moderate
MAO inhibitors
Possible interaction
Moderate
Traditional Chinese Medicine
Commonly Used Preparations
Herb
English Name
Potential Interactions
當歸 (Dang Gui)
Angelica
Anticoagulants
人參 (Ren Shen)
Ginseng
Multiple (see above)
甘草 (Gan Cao)
Liquorice
Antihypertensives, Corticosteroids
麻黃 (Ma Huang)
Ephedra
Stimulants, Antihypertensives
Considerations in Singapore
TCM is commonly used alongside Western medicine
Patients may not disclose herbal use
Ask specifically about TCM during medication review
Ayurvedic Preparations
Preparation
Potential Concerns
Ashwagandha
Sedative interactions
Triphala
May contain heavy metals
Guggul
Anticoagulant interactions
Supplement Categories
Cardiovascular
Supplement
Interacts With
Fish oil (high dose)
Anticoagulants
Coenzyme Q10
Warfarin
Hawthorn
Cardiac medications
Metabolic
Supplement
Interacts With
Chromium
Diabetes medications
Bitter melon
Diabetes medications
Cinnamon
Diabetes medications
Neurological
Supplement
Interacts With
Valerian
CNS depressants
Kava
CNS depressants, Hepatotoxic drugs
Melatonin
CNS depressants, Anticoagulants
Clinical Recommendations
For Healthcare Providers
Always ask about herbal and supplement use
Check for interactions before prescribing
Consider discontinuation before surgery
Monitor for unexpected effects
Document all supplements in the record
For Patients
Inform providers about all supplements
Don't assume "natural" means safe
Be cautious with new medications
Stop herbs before planned surgery (usually 2 weeks)
Report any unusual symptoms
Resources
Resource
Description
Natural Medicines Database
Comprehensive interaction checker
NIH National Center for Complementary and Integrative Health
Evidence-based information
DrugBank
Herbal interaction data
Safety Notice
Drug-herb interaction data is often limited. Always consult healthcare providers before combining herbal products with prescription medications. This information is for educational purposes only.