Actions and Interactions

Because they have medicinal properties, herbs should be considered drugs when it comes to interactions. Just as you would do (or should do) when taking prescription or OTC pharmaceuticals, you should make sure that the herbs you're taking aren't interfering with any drugs — or with each other.

Herbs with Sedative Properties

Several herbs act as sedatives (they induce relaxation and sleepiness) and can have an additive effect — that is, they'll increase the action of another agent — when combined with other sedatives, including alcohol.

Don't combine sedating drugs like antihistamines (including those in antimotion-sickness meds) or insomnia remedies with herbs like gotu kola (Centella asiatica), kava (Piper methysticum), or valerian (Valeriana officinalis), which are sedating on their own. Other sedating herbs include:

  • Ashwagandha (Withania somnifera)

  • Calendula (Calendula officinalis)

  • Chamomile (Matricaria recutita)

  • Eleuthero (Eleutherococcus senticosus)

  • Gotu kola (Centella asiatica)

  • Hops (Humulus lupulus)

  • Kava (Piper methysticum)

  • Lemon balm (Melissa officinalis)

  • Passionflower (Passiflora incarnata)

  • Sage (Salvia officinalis, S. lavandulaefolia)

  • Valerian (Valeriana officinalis)

  • The government requires nonprescription products to carry a “Drug Facts” label that includes the active ingredients, uses, warnings, and directions (dosage instructions). Packaged herbals are simply required to list the product's ingredients on a “Supplement Facts” label (and bulk herbs may have no label at all), meaning you'll have to do your own research before taking them.

    Herbal Stimulants

    Several herbs contain caffeine or other chemicals that stimulate the central nervous system. They can have additive effects when combined with other stimulants. They include:

  • Asian ginseng (Panax ginseng)

  • Cocoa (Theobroma cacao)

  • Coffee (Coffea arabica)

  • Guarana (Paullinia cupana)

  • Mate (Ilex paraguariensis)

  • Tea (Camellia sinensis)

  • Herbs and Blood Sugar

    Several herbs work to lower glucose levels, but they can reduce blood sugar too much when combined with diabetes drugs, which do the same thing. Herbs with hypoglycemic potential include:

  • Alfalfa (Medicago sativa)

  • Aloe (Aloe vera), when used internally

  • Asian ginseng (Panax ginseng)

  • Bilberry (Vaccinium myrtillus)

  • Cinnamon (Cinnamomum verum, C. aromaticum)

  • Eleuthero (Eleutherococcus senticosus)

  • Eucalyptus (Eucalyptus globulus)

  • Fenugreek (Trigonella foenum-graecum)

  • Flax (Linum usitatissimum)

  • Ginger (Zingiber officinale)

  • Horse chestnut (Aesculus hippocastanum)

  • Konjac (Amorphophallus konjac, A. rivieri)

  • Kudzu (Pueraria lobata)

  • Nettle (Urtica dioica)

  • Onion (Allium cepa)

  • Sage (Salvia officinalis, S. lavandulaefolia)

  • Tinospora (Tinospora cordifolia)

  • Cardioactive Herbs

    Several herbs exert a direct effect on heart function, and so should be avoided by anyone with a heart condition (or anyone taking drugs to treat a heart condition). These include:

  • Asian ginseng (Panax ginseng)

  • Coleus (Coleus forskohlii, Plectranthus barbatus)

  • Danshen (Salvia miltiorrhiza)

  • Devil's claw (Harpagphytum procumbens)

  • Hawthorn (Crataegus monogyna, C. oxyacantha)

  • Grapefruit (Citrus paradisi) is used as both a medicinal herb and a breakfast drink, but it can cause big problems if it's combined with a variety of medications, including oral contraceptives and prescription allergy, anxiety, and insomnia drugs. Doctors suggest you skip the supplemental grapefruit if you're taking any medications — and wash your medications down with water instead.

    Anticoagulant/Antiplatelet Action

    Several herbs affect platelet aggregation, or clotting of your blood, and so should be avoided if you're taking medicines that do the same thing, such as clopidogrel (Plavix) and warfarin (Coumadin). You should discontinue using them at least two weeks before any surgery. They include:

  • Andrographis (Andrographis paniculata)

  • Asian ginseng (Panax ginseng)

  • Borage (Borago officinalis)

  • Cayenne (Capsicum annuum, C. frutescens)

  • Chamomile (Matricaria recutita)

  • Coleus (Coleus forskohlii, Plectranthus barbatus)

  • Danshen (Salvia miltiorrhiza)

  • Dong quai (Angelica sinensis)

  • Eleuthero (Eleutherococcus senticosus)

  • Evening primrose (Oenothera biennis)

  • Fenugreek (Trigonella foenum-graecum)

  • Feverfew (Tanacetum parthenium)

  • Flax (Linum usitatissimum)

  • Garlic (Allium sativum)

  • Ginger (Zingiber officinale)

  • Ginkgo (Ginkgo biloba)

  • Horse chestnut (Aesculus hippocastanum)

  • Kudzu (Pueraria lobata)

  • Licorice (Glycyrrhiza glabra)

  • Onion (Allium cepa)

  • Pineapple (Ananas comosus)

  • Red clover (Trifolium pratense)

  • Reishi (Ganoderma lucidum)

  • Turmeric (Curcuma longa)

  • Willow (Salix alba)

  • Don't combine OTC decongestants with stimulant herbs like mate (Ilex paraguariensis) or guarana (Paullinia cupana). All of these things can raise your blood pressure and cause other side effects (like increased heart rate, jittery nerves, or irritability).

    Hormonal Effects

    Some herbs contain chemicals called phytoestrogens that act like the human hormone estrogen. Others affect estrogen levels through different mechanisms. Generally speaking, pregnant and nursing women, men, and children should avoid them, as should anyone with a hormone-dependent disease or condition. You also should use caution when combining them with oral contraceptives. They include:

  • Alfalfa (Medicago sativa)

  • Black cohosh (Actaea racemosa, Cimicifuga racemosa)

  • Dong quai (Angelica sinensis)

  • Flax (Linum usitatissimum)

  • Kudzu (Pueraria lobata)

  • Red clover (Trifolium pratense)

  • Saw palmetto (Serenoa repens)

  • Soy (Glycine max)

  • Vitex (Vitex agnus-castus)

  • Immunity Modulators

    Some herbs can affect your immune system, and therefore shouldn't be combined with immunosuppressant drugs. They include:

  • Alfalfa (Medicago sativa)

  • Andrographis (Andrographis paniculata)

  • Ashwagandha (Withania somnifera)

  • Astragalus (Astragalus membranaceus)

  • Cat's claw (Uncaria guianensis, U. tomentosa)

  • Cordyceps (Cordyceps sinensis)

  • Elderberry (Sambucus nigra)

  • Eleuthero (Eleutherococcus senticosus)

  • Maritime pine (Pinus pinaster)

  • Neem (Azadirachta indica)

  • Reishi (Ganoderma lucidum)

  • Tinospora (Tinospora cordifolia)

  • Immunity Stimulants

    Some herbs increase immune function, and shouldn't be taken by people with autoimmune disorders:

  • Barberry (Berberis vulgaris)

  • Echinacea (Echinacea purpurea)

  • Goldenseal (Hydrastis canadensis)

  • Tinospora (Tinospora cordifolia)

  • Herbs and Hyperlipidemia

    Several herbs work to lower cholesterol — and can increase the effect of pharmaceuticals that do the same; they also can skew laboratory lipid test results. They include:

  • Alfalfa (Medicago sativa)

  • Flax (Linum usitatissimum)

  • Garlic (Allium sativum)

  • Guggul (Commiphora wightii, C. mukul)

  • Hawthorn (Crataegus monogyna, C. oxyacantha)

  • Oat (Avena sativa)

  • Psyllium (Plantago ovata, P. psyllium)

  • Herbs and Hypertension

    Several herbs have hypotensive effects and so shouldn't be combined with other blood pressure-lowering agents. They include:

  • Andrographis (Andrographis paniculata)

  • Cat's claw (Uncaria guianensis, U. tomentosa)

  • Coleus (Coleus forskohlii, Plectranthus barbatus)

  • Garlic (Allium sativum)

  • Hawthorn (Crataegus monogyna, C. oxyacantha)

  • Nettle (Urtica dioica)

  • Olive (Olea europaea)

  • Pomegranate (Punica granatum)

  • Reishi (Ganoderma lucidum)

  • Valerian (Valeriana officinalis)

  • Others can cause a rise in blood pressure. They include:

  • Licorice (Glycyrrhiza glabra)

  • Sage (Salvia officinalis, S. lavandulaefolia)

  • Yohimbe (Pausinystalia yohimbe)

  • Liver Concerns

    Some herbs can adversely affect liver function — they're potentially hepatotoxic — and shouldn't be used concurrently. They also shouldn't be combined with hepatotoxic pharmaceuticals such as acetaminophen (Tylenol). These agents can also interfere with liver function tests and might exacerbate liver problems in some people. Herbs that can affect liver function include:

  • Black cohosh (Actaea racemosa, Cimicifuga racemosa)

  • Borage (Borago officinalis)

  • Butterbur (Petasites hybridus)

  • Cinnamon (Cinnamomum verum, C. aromaticum)

  • Comfrey (Symphytum officinale)

  • Gotu kola (Centella asiatica)

  • Kava (Piper methysticum)

    1. Home
    2. Herbal Remedies Guide
    3. Safety and Efficacy
    4. Actions and Interactions
    Visit other About.com sites: