Herb Interaction Potential Effects
Chamomile
Chamomilla recutita
Anticonvulsants.
Barbiturates & Sedatives.
Benzodiazepines
Increase in bruising and bleeding.
Drowsiness.
Devils Claw
Harpagophytum procumbens
Warfarin.
Antiarrythmic drugs.
Aspirin.
Increase in bruising and bleeding. May increase arrythmia
Dong Quai
Angelica sinensis
Warfarin.
Oestrogen/HRT.
Hormone-sensitive tumours. Pregnancy.
Increase in bruising and bleeding.
Potential excess of oestrogen.
May cause uterine contractions
Echinacea spp.
 
Hepato-toxic agents (e.g. Methotrexate).
Immune suppressant medication.
Possible liver toxicity.
Counteracts effect of immune suppressants.
Feverfew
Tanacetum parthenium
Anticoagulants e.g. Warfarin.
Pregnancy.
Increased risk of bleeding, bruising and haemorrhage.
Garlic
Allium sativum
NSAIDs – Non-steroidal anti-inflammatory drugs.
Saquinivir.
Anticoagulats.
Antiplatelet drugs.
Antihypertensive drugs.
Bleeding abnormalities.
Decreases efficacy of saquinavir.
May increase bleeding.
Ginger
Zingiber officialis
Warfarin.
Antiplatelet drugs.
High doses in pregnancy.
Risk of post-operative bleeding, haemorrhage.   
Ginkgo
Ginkgo biloba
(circulatory stimulant)
Anticoagulants (warfarin).
NSAIDs.
Anticonvulsants (phenytoin).
Monoamine oxidase inhibitors (MAOIs).
May increase bleeding.
Reduced efficacy of anticonvulsants.
Intensify effects of MAOIs increasing side effects 
Ginseng (Siberian)
Eleutherococcus senticosus
Anticoagulants (warfarin).
NSAIDs.
Estrogen replacement therapy.
MAOIs.
May decrease effectiveness.
Increase heart rate or blood pressure.
May cause bleeding in women post-menopause.
Increase side effects of MAOIs
Caffeine-like palpitations, tremors, insomnia
Ginseng (Korean)
Panax ginseng
Stimulants e.g. caffeine
Hypertensives
Insomnia, anxiety, irritability, increase high blood pressure, tremor, hysteria, mania, headaches, palpitations, diarrhoea, skin eruptions, menstrual abnormalities              
Guarana
Paulinia cupana
(contains caffeine)
Anti-anxiety agents.
Anti-hypertensives.
Sedatives/hypnotics/tranquilisers.
Counteract effects of these medicines.
Liquorice
Glycyrrhiza glabra
Antihypertensives.
Prednisolone.
Hydrocortisone.
Diuretics.
Cardiac glycosides, e.g. Digitalis/Digoxin
Increased levels of steroids (reduced clearance).
Loss of potassium.
Increased sensitivity to digitalis glycosides.
Passionflower
Passiflora incarnata
Benzodiazepines.
Barbiturates.
Alcohol.
Antipsychotics.
Antidepressants.
Excess sedation, coma
Rosemary
Rosmarinus officinalis
Pregnancy. Anti-implantation effect, possibly abortifacient.
Saw palmetto
Serenoa serrulata
Oestrogen replacement therapy and oral contraceptives.
Pregnancy.
Hormonal effects.
St John’s Wort
Hypericum perforatum
Antidepressants.
Anticonvulsants.
HIV protease inhibitors.
Oral contraceptive pill.
Serotonin excess.
Increased frequency.
Decreased serum levels.
Mid-cycle bleeding.
Valerian
Valariana officinalis
Observe with sedatives. Possible excess sedation.
 Wormwood Anticonvulsants. Insomnia, nightmares, convulsions,
neurotoxic in high doses, or if taken over long periods, do not take regularly