Safety tool · 69 plants

Herb–drug interactions: which plants can cause problems with your medicine?

Plants contain active substances just as medicines do. Some can strengthen your medicine’s effect, some weaken it, and some add to its side effects. Below, the interactions reported in the catalog are grouped by medicine.

Medicine groups

Blood thinners (warfarin, aspirin and others) (20)
Diabetes medicines and insulin (20)
Blood pressure medicines (20)
Heart medicines (digoxin, heart rhythm drugs) (14)
Antidepressants and migraine medicines (triptans) (16)
Sleeping pills, sedatives and alcohol (11)
Birth control pills and hormone therapy (4)
Immunosuppressants and transplant medicines (7)
Diuretics (water pills) (9)
Lithium (5)
Seizure (epilepsy) medicines (7)
Medicines broken down by, or straining, the liver (12)
Corticosteroids (4)
Stimulants and caffeine (9)
Antibiotics (4)
Cancer and HIV medicines (4)
Iron supplements (2)
Stomach acid reducers (1)
All oral medicines (absorption effects) (3)

Blood thinners (warfarin, aspirin and others)

Plant	Possible interaction
Borage	GLA may increase bleeding; stop the oil capsules before surgery.
Cat’s claw	May increase bleeding risk.
Cinchona	Increases bleeding risk.
Clove	Eugenol affects platelets and may increase bleeding risk.
Copaiba	May increase bleeding risk in theory.
Fenugreek	May increase bleeding risk.
Ginkgo	May increase bleeding risk.
Ginseng	May weaken warfarin.
Goji	Cases of bleeding and raised INR have been reported; avoid together or check INR often.
Hemp	CBD and THC may raise drug levels.
Horse chestnut	Thought to increase bleeding risk; use together only under medical supervision.
Pau d’arco	Lapachol counteracts vitamin K; risk of bleeding.
Reishi mushroom	May slow clotting; bleeding risk may rise.
Rue	Contains coumarin derivatives; may increase bleeding risk.
Sacha inchi	Omega-3 fatty acids at high doses may increase bleeding tendency.
Saffron	May increase bleeding tendency at high doses.
St John’s wort	Lowers drug levels; risk of clots or heart rhythm problems.
Turmeric	May increase bleeding risk.
White willow	Salicylates may increase bleeding risk.
Yarrow	May increase bleeding risk.

Diabetes medicines and insulin

Plant	Possible interaction
Aloe vera	Oral aloe may lower blood sugar.
Ashwagandha	Can lower blood sugar and blood pressure.
Bitter melon	Can lower blood sugar dangerously.
Chanca piedra	Can lower blood sugar.
Chuchuhuasi	Traditionally prepared by steeping in alcohol.
Cinchona	Can lower blood sugar.
Cinnamon	Can lower blood sugar.
Eucalyptus	Can lower blood sugar.
Fenugreek	Lowers blood sugar; risk of hypoglycaemia.
Ginseng	Lowers blood sugar.
Goji	May lower blood sugar and blood pressure; effects can add up.
Goldenberry	Limited data suggest the fruit lowers blood sugar.
Greek sage	Can lower blood sugar; risk of hypoglycaemia with the drug.
Horse chestnut	Animal data suggest it may lower blood sugar; monitor glucose.
Juniper	Can lower blood sugar.
Neem	May lower blood sugar; risk of hypoglycaemia.
Reishi mushroom	May lower blood pressure and blood sugar; effects can add up.
Roseroot	May affect blood sugar and blood pressure.
Soursop	May lower blood pressure and blood sugar.
Turmeric	Can lower blood sugar.

Blood pressure medicines

Plant	Possible interaction
Abuta	Can lower blood pressure.
Ashwagandha	Can lower blood sugar and blood pressure.
Bitter orange	Synephrine may raise blood pressure; it can be dangerous with MAO inhibitors.
Cat’s claw	Can lower blood pressure.
Chacruna	Swings in heart rate and blood pressure.
Chanca piedra	Can lower blood pressure.
Coca	The mild stimulant effect may work against the drug.
Ephedra	Raises blood pressure and counteracts the drug.
European mistletoe	May increase the effect by lowering blood pressure.
Goji	May lower blood sugar and blood pressure; effects can add up.
Hawthorn	May add to blood-pressure-lowering and vessel-widening effects.
Licorice	Raises blood pressure and weakens the drug.
Peyote	Raises blood pressure and heart rate.
Reishi mushroom	May lower blood pressure and blood sugar; effects can add up.
Roseroot	May affect blood sugar and blood pressure.
Saffron	Can lower blood pressure slightly.
San Pedro cactus	Raises blood pressure and heart rate.
Soursop	May lower blood pressure and blood sugar.
Yarrow	May increase the effect.
Yopo	Sudden changes in blood pressure and heart rate.

Heart medicines (digoxin, heart rhythm drugs)

Plant	Possible interaction
Aloe vera	Low potassium raises the risk of toxicity.
Buckthorn	Low potassium raises the risk of toxicity.
Chacruna	Swings in heart rate and blood pressure.
Cinchona	Risk of dangerous heart rhythm disturbance.
Coca	The mild stimulant effect may work against the drug.
Goldenseal	May raise drug levels.
Hawthorn	May increase the effect.
Licorice	Low potassium raises the risk of digoxin toxicity.
Oleander	Oleandrin acts like digoxin; together they can cause fatal heart rhythm disturbance.
Peyote	Raises blood pressure and heart rate.
San Pedro cactus	Raises blood pressure and heart rate.
Senna	Low potassium raises the risk of toxicity.
St John’s wort	Lowers drug levels; risk of clots or heart rhythm problems.
Yopo	Sudden changes in blood pressure and heart rate.

Antidepressants and migraine medicines (triptans)

Plant	Possible interaction
Ayahuasca vine	Serotonin syndrome: can be fatal. The risk lasts for weeks after stopping these drugs.
Bitter orange	Synephrine may raise blood pressure; it can be dangerous with MAO inhibitors.
Chacruna	Drunk with ayahuasca, so the same serotonin syndrome risk applies.
Coca	Risk of raised blood pressure.
Ephedra	Risk of hypertensive crisis.
Ginseng	Insomnia, headache and restlessness have been reported.
Goldenseal	May raise drug levels.
Henbane	Act the same way; poisoning symptoms multiply.
Nutmeg	Myristicin is a weak MAO inhibitor; interaction is possible at high doses.
Peyote	May change the effect of mescaline unpredictably.
Roseroot	Thought to act through serotonin; data on combined use are insufficient.
Saffron	Extra mood effect; ask a doctor before combining at supplement doses.
San Pedro cactus	May change the effect of mescaline unpredictably.
St John’s wort	Risk of serotonin syndrome.
Syrian rue	Harmala alkaloids inhibit the MAO enzyme; combining them can cause serotonin syndrome.
Yopo	Risk of serotonin syndrome with bufotenine and DMT.

Sleeping pills, sedatives and alcohol

Plant	Possible interaction
Ashwagandha	May increase drowsiness.
Chiric sanango	Its effects on the nervous system are unpredictable.
Chuchuhuasi	Traditionally prepared by steeping in alcohol.
Fly agaric	Muscimol acts through GABA; risk of losing consciousness increases.
French lavender	Calming effects can add up.
Greek sage	May increase the effect.
Hemp	Drowsiness and slowed reactions increase.
Mandrake	Increases confusion.
Nutmeg	At high doses, nutmeg’s effects may be stronger.
Opium poppy	The risk of stopped breathing and loss of consciousness multiplies; can be fatal.
Yarrow	May increase the effect.

Birth control pills and hormone therapy

Plant	Possible interaction
Black cohosh	Ask the oncologist before combining.
Chaste tree	Acts on hormone balance; may change the effect.
Fennel	Its weak oestrogen-like effect could interact in theory.
St John’s wort	Speeds up liver enzymes (CYP3A4) and weakens the pill; unintended pregnancies have been reported.

Immunosuppressants and transplant medicines

Plant	Possible interaction
Ashwagandha	May interact by stimulating immunity.
Cat’s claw	May weaken the drug by stimulating immunity.
Elder	Theoretical interaction, as it may stimulate immunity.
European mistletoe	May stimulate immunity.
Neem	May stimulate immunity and weaken the drug.
Reishi mushroom	Its immune-stimulating effect may weaken the drug.
St John’s wort	Lowers drug levels; organ rejection has been reported.

Diuretics (water pills)

Plant	Possible interaction
Aloe vera	Leaf latex increases potassium loss.
Buckthorn	Increase potassium loss.
Chanca piedra	Its diuretic effect may change lithium levels.
Copaiba	Its diuretic effect may add up.
Elder	The flower’s mild diuretic effect may add up.
Juniper	Diuretic effects add up; salt loss may increase.
Licorice	Increases potassium loss.
Oleander	Lower potassium and worsen poisoning.
Senna	Increase potassium loss.

Lithium

Plant	Possible interaction
Ayahuasca vine	Serious interaction through serotonin.
Chanca piedra	Its diuretic effect may change lithium levels.
Guaraná	Caffeine changes the level or effect of these drugs.
Juniper	The diuretic effect may raise lithium levels.
Yarrow	Its diuretic effect may raise lithium levels.

Seizure (epilepsy) medicines

Plant	Possible interaction
Borage	There are reports that GLA-containing oils may lower the seizure threshold.
Chiric sanango	Its effects on the nervous system are unpredictable.
French lavender	The camphor-rich oil may lower the seizure threshold.
Ginkgo	Ginkgotoxin in the seeds may lower the seizure threshold.
Greek sage	Thujone can lower the seizure threshold and weaken the drug at high doses.
Hemp	CBD changes drug levels and may raise liver enzymes.
Wormwood	Thujone lowers the seizure threshold.

Medicines broken down by, or straining, the liver

Plant	Possible interaction
Bearberry	Hydroquinone adds strain on the liver.
Bitter melon	Lab studies show it affects drug transport.
Black cohosh	Rare cases of liver injury have been reported.
Borage	Pyrrolizidine alkaloids raise the risk of liver damage.
Cat’s claw	Lab studies show it affects this enzyme.
Cinnamon	Coumarin in cassia adds strain on the liver.
Eucalyptus	Cineole speeds up liver enzymes and may lower some drug levels.
Goldenseal	May raise drug levels.
Mapacho	Tobacco smoke lowers the levels of these drugs.
Matico	Safrole and dillapiole may affect liver enzymes.
Muña	Pulegone adds strain on the liver.
Pennyroyal	Pulegone increases liver damage.

Corticosteroids

Plant	Possible interaction
Aloe vera	Leaf latex increases potassium loss.
Buckthorn	Increase potassium loss.
Licorice	May increase effects and side effects.
Senna	Increase potassium loss.

Stimulants and caffeine

Plant	Possible interaction
Ayahuasca vine	Dangerous rise in blood pressure and heart rate.
Bitter orange	With synephrine, heart rate and blood pressure may rise.
Coca	Stimulant effects add up; risk of palpitations.
Ephedra	Multiplies the risk of heart attack and stroke.
Ginseng	Stimulant effects may add up.
Guaraná	Caffeine doses add up.
Peyote	Raises blood pressure and heart rate.
San Pedro cactus	Raises blood pressure and heart rate.
Syrian rue	Together with MAO inhibition, blood pressure and heart rate can rise dangerously.

Antibiotics

Plant	Possible interaction
Autumn crocus	Slow the breakdown of colchicine or increase the risk of muscle damage.
Fennel	Taken at the same time, may reduce absorption.
Guaraná	Slow the clearance of caffeine.
Rue	Increases the risk of phytophotodermatitis.

Cancer and HIV medicines

Plant	Possible interaction
Black cohosh	Ask the oncologist before combining.
European mistletoe	Mistletoe extracts are used as supportive cancer care in some countries; only with the oncologist’s knowledge.
St John’s wort	Can lower drug levels enough to make treatment fail.
Turmeric	Ask the oncologist before combining with chemotherapy.

Iron supplements

Plant	Possible interaction
Pennyroyal	Its tea may reduce iron absorption.
Turmeric	High doses may reduce iron absorption.

Stomach acid reducers

Plant	Possible interaction
Wormwood	Bitter compounds increase stomach acid and may weaken the effect.

All oral medicines (absorption effects)

Plant	Possible interaction
Buckthorn	Faster bowel transit may reduce absorption.
Fenugreek	Its fibre may delay absorption; leave 2 hours between them.
Senna	Faster bowel transit may reduce absorption.

Take special care

St John’s wort is the best-known plant that weakens many medicines, including birth control pills, blood thinners and some heart and transplant drugs. Taken with antidepressants it can cause serotonin syndrome.