One of the most common ways of classifying medicinal plants is to identify their actions, for example whether they are sedative, antiseptic, or diuretic, and the degree to which they affect different body systems. Herbs often have a pronounced action on a particular body system, for example a plant that is strongly antiseptic in the digestive tract may be less so in the respiratory tract. Examples of how herbs work on the body are given below.

Skin

Antiseptics, e.g., tea tree (Melaleuca alternifolia), disinfect the skin. Emollients, e.g., marshmallow (Althaea officinalis), reduce itchiness, redness, and soreness. Astringents, e.g., witch hazel (Hamamelis virginiana), tighten the skin. Depuratives, e.g., burdock (Arctium lappa), encourage removal of waste products. Healing and vulnerary herbs, e.g., comfrey (Symphytum officinale) and calendula (Calendula officinalis), aid the healing of cuts, wounds, and abrasions.

Immune system

Immune modulators, e.g., echinacea (Echinacea spp.) and pau d’arco (Tabebuia spp.), encourage the immune system to ward off infection.

Respiratory system

Antiseptics and antibiotics, e.g., garlic (Allium sativum), help the lungs resist infection. Expectorants, e.g., elecampane (Inula helenium), stimulate the coughing up of mucus. Demulcents, e.g., coltsfoot (Tussilago farfara), soothe irritated membranes. Spasmolytics, e.g., visnaga (Ammi visnaga), relax bronchial muscles.

Endocrine glands

Adaptogens, e.g., ginseng (Panax ginseng), help the body adjust to external pressures and stress. Hormonally active herbs, e.g., chaste tree (Vitex agnus-castus), stimulate production of sex and other hormones. Emmenagogues, e.g., black cohosh (Cimicifuga racemosa), encourage or regulate menstruation.

Urinary system

Antiseptics, e.g., buchu (Barosma betulina), disinfect the urinary tubules. Astringents, e.g., horsetail (Equisetum arvense), tighten and protect the urinary tubules. Diuretics, e.g. cornsilk (Zea mays), stimulate the flow of urine.

Musculoskeletal system

Analgesics, e.g., yellow jasmine (Gelsemium Sempervirens), relieve joint and nerve pain. Anti-inflammatories, e.g., white willow (Salix alba), reduce swelling and pain in joints. Antispasmodics, e.g., cinchona (Cinchona spp.), relax tense and cramped muscles.

Nervous system

Nervines, e.g., rosemary (Rosmarinus officinalis), support and strengthen the nervous system. Relaxants, e.g., lemon balm (Melissa officinalis), relax the nervous system. Sedatives, e.g., mistletoe (Viscum album), reduce nervous activity. Stimulants, e.g., kola nut (Cola acuminata), increase nervous activity. Tonics, e.g., oats (Avena sativa), improve nerve function and tone, and help to restore the nervous system as a whole.

Circulation & heart

Cardiotonics, e.g., dan shen (Salvia miltiorrhiza), vary in action. Some slow heartbeat rate, while others increase it. Some improve the regularity and strength of the heart’s contractions. Circulatory stimulants, e.g., cayenne (Capsicum frutescens), improve the circulation of blood to the extremities. Diaphoretics, e.g., ju hua (Chrysanthemum x morifolium), encourage blood flow to the surface of the body, promote sweating, and lower blood pressure. Spasmolytics, e.g., cramp bark (Viburnum opulus), relax the muscles, helping to lower blood pressure.

Digestive organs

Antiseptics, e.g., ginger (Zingiber officinale), protect against infection. Astringents, e.g., bistort (Polygonum bistorta), tighten up the inner lining of the intestines and create a protective coating over them. Bitters, e.g., wormwood (Artemisia absinthium), stimulate secretion of digestive juices by the stomach and intestines. Carminatives, e.g., sweet flag (Acorus calamus), relieve gas and cramps.

Cholagogues, e.g, fringe tree (Chionanthus virginicus), improve the flow of bile into the intestines. Choleretics, e.g., artichoke (Cynara scolymus), stimulate secretion of bile by the liver. Demulcents, e.g., psyllium (Plantago spp.), soothe the digestive system and protect against acidity and irritation.

Hepatics, e.g., bupleurum (Bupleurum chinense), prevent liver damage. Laxatives, e.g., senna (Cassia senna), stimulate bowel movements. Stomachics, e.g., cardamom (Elettaria cardamomum), protect and support the stomach.