A diuretic is a remedy that increases the secretion & elimination of urine from the body. A diuretic is a substance that will increase the volume of urine produced, by promoting the excretion of salts and water. They are used to reduce edema especially in heart, liver or kidney disorders, to treat high blood pressure, and occasionally to treat glaucoma.
Another action of diuretics is detoxification and purgation through the urine. Generally they are bitter, astringent or pungent in taste. All diuretics tend to increase the dryness associated with Vata Dosha.
Diuretics decrease water and reduce Kapha, and also reduce Pitta, since urination is also a way of relieving heat from the body, of removing acid and toxins from the blood, a way of cooling and purifying the blood.
Heating and drying herbs, pungent in taste, bring water up and out of the body through the process of sweating – diaphoretic action. They also work by relieving mucus by their expectorant quality. Just as water evaporates upwards by the action of fire, heating and drying herbs purify the system. Facially-accumulated water and water in the head and chest are often better reduced by diaphoretic and expectorant herbs.
Diuretic action is generally cooling and drying, the opposite of the qualities of Pitta which are heat and moisture. For this reason, diuretics dispel damp heat, as in diarrhea and dysentery, and cool down not only the kidneys and bladder, but also the liver and gallbladder. In increasing urination, they help dispel kidney and bladder stones, and also stones of the gallbladder. Such stone-dispelling herbs are called lithotriptic.
In their more specific anti-Kapha action, diuretic herbs dispel edema and water accumulation in the tissues, particularly in the lower half of the body. They help decrease weight, particularly when weight is mainly due to excess water. They stimulate bladder and kidney function, but are seldom actually a tonic or nutritive to the kidneys. Their drying action may cause constipation or dryness of the skin. Scanty urination without water accumulation requires a moistening, not a drying therapy, and for that condition, diuretic herbs are usually contraindicated.
Vata constitution needs to increase urine by increasing water in the tissue – not a diuretic but a tonic or nutritive therapy. Diuretics are probably the strongest herbs to aggravate Vata, and are contraindicated in conditions of convalescent debility and dehydration.
Diuretics can be divided into cooling and heating kinds, the cooling type are the majority. Cooling diuretics are also often cooling diaphoretics, alteratives or antipyretic herbs, useful in fevers and infectious diseases, particularly those involving the urino-genital tract or the liver and gallbladder.
Warming diuretics are often warming diaphoretics, stimulants and expectorants and may have antirheumatic action. They are contraindicated in Pitta conditions of kidney or gallbladder inflammation unless they are balanced out by a majority of cooling herbs.
A few diuretics are cooling and moistening, apart from their drying action in diuresis, and have a soothing effect upon the mucous membranes of the urinary system. Examples are marshmallow, barley or tribulusterrestris (Gokshura). Often one of these herbs is added to a diuretic formula to soothe and protect the kidneys from the drying and scraping action of diuretic herbs that can cause irritation and discomfort.
Typical cooling diuretics: asparagus, barley, burdock, coriander, cornsilk, dandelion, fennel, gokshura, lemon grass, marshmallow, punarnava, spearmint.
Typical warming diuretics: ajuwan, cinnamon, garlic, mustard, parsley
How do diuretics work
Stimulating diuretics work by irritating the kidneys so that they try to flush away the offending substance (eg. Juniperuscommunis acts in this way). They also include caffeine containing herbs (eg. tea & coffee) that increase the blood flow in the kidneys by effects on the heart or elsewhere in the body. Because there is more blood passing through the kidney, more urine is therefore produced. Constituents that irritate the resorption mechanism in this way are often volatile oils, saponins or alkaloids.
Betulaalba (Silver birch)
Osmotic diuretics work via many different means, but often cause diuresis due to constituents such as mainly mucilage & polysaccharides which cause a nerve reflex reaction through the gut lining (via the vagus) to thin & loosen mucous secretions to be excreted via the kidney. As larger and/or unmetabolized sugars pass into the urine, this change in osmotic pull causes more water to be lost (eg. Agropyronrepens&Zea Mays act in this way).
Agropyronrepens (Couch Grass)
Zea mays (Corn silk)
Althea officinalis (Marshmallow)
Taraxacumofficinalis folia (Dandelion leaf)
Cardiac or peripheral circulatory stimulants work by increasing renal blood flow and hence the glomerular filtration rate. Up to a certain point any excess glomerular filtrate can be reabsorbed from the kidney tubules, but if it is too high then the urine volume will increase. Herbs that increase the cardiac output and/or stimulate peripheral circulation include:
Crataegus spp. (Hawthorne)
Convallariamajalis (Lily of the Valley)